Date Calculator (Add or Subtract Days, Weeks, Months and Years)

Enter a start date and the years, months, weeks and days to add or subtract. You get both the later date and the earlier date, with the day of the week. To skip weekends, enter a number only in the business days field at the bottom.

Start date

Years

Months

Weeks

Days

Business days (skips weekends, use alone)

Fields you do not need can be left blank (or 0). When you use the business days field, leave years, months, weeks and days blank. (Business days skip only Saturdays and Sundays, not holidays.)

Result

Enter a start date and the number of days (or weeks, months, years) in the fields on the left and press "Calculate". The result will appear here.

[ CLOSE ]

What you can do on this page
What is this calculation used for?
How to Use
Formula
Symbols and terms
- Symbols
- Terms
Good to know before you start
How to calculate it in Excel
How to calculate it in Google Sheets
How to calculate it in Python
How to write it in LaTeX and other math languages (copy and paste)
How to have ChatGPT do the calculation
DataChef Features
Related Features
NumberChef Calculators List

What you can do on this page

Add years, months, weeks and days to a start date, or subtract them, and get both the later date and the earlier date with the day of the week
Answers questions such as "What is 90 days from today?", "What date is 2 weeks before the deadline?" and "What is the date 1 year and 6 months from now?"
Also counts business days, skipping Saturdays and Sundays, to find the date a number of business days later or earlier (holidays are not skipped)
A plain-language explanation of month-end cases such as "What is 1 month after January 31?" and copy-and-paste formulas for Excel, Google Sheets (the EDATE and WORKDAY functions) and Python are all on this page

"1 month later" and "1 year later" land on the same day number in the next month or year. If that month has no such day, the result is the last day of the month (for example, 1 month after January 31 is February 28, or 29 in a leap year). Business days skip only Saturdays and Sundays, not federal holidays or company days off.

What is this calculation used for?

Getting payment due dates right ("Net 30" and end-of-month terms)

An invoice with "Net 30" terms - payment due within 30 days of the invoice date - is exactly a "days later" calculation. For an invoice dated April 15, 2026, the due date 30 days later is Friday, May 15.
Terms such as "due at the end of the following month" use the "months later" calculation. With money, missing a due date by even one day can hurt your credit, so it is safer to check with a calculation than to count on your fingers.

Counting shipping and processing times in business days ("ships within 5 business days")

"Ships within 5 business days" for online orders, or "processing takes 5 to 7 business days" at a bank or government office, means counting business days and skipping weekends. If you order on Friday, October 2, 2026, 5 business days later is the next Friday (October 9), after skipping the Saturday and Sunday.
Real deadlines also depend on holidays and company days off, so use this calculator's result (weekends only) as a guide and check your calendar for holidays in between.

Planning doctor visits, medicine and vaccines ("come back in 2 weeks")

Medical schedules such as "follow-up in 2 weeks" or "next dose 4 weeks later" are often given in weeks. 2 weeks later is 14 days later, so it falls on the same weekday as the start date (if June 1 is a Monday, 2 weeks later, June 15, is a Monday too).
Knowing the date when a 28-day supply of medicine runs out, or when to book the next appointment, helps you avoid missed doses and late bookings.

Working back from a move-out date (notice "one month" or "30 days" before)

Many leases require written notice one month, or 30 or 60 days, before you move out. If you want to move out on October 31, 2026, one month before is September 30 (September has no 31st, so it is rounded to the end of the month), while 30 days before is October 1.
Notice given at the last minute can cause trouble, so calculate the date first and give yourself some extra time. The wording of your lease decides how the deadline is counted, so check your lease for the exact deadline.

Estimating a due date (280 days after the last period)

A common way to estimate a due date (Naegele's rule) is 280 days, or 40 weeks 0 days, after the first day of the last menstrual period. For example, if that day is January 1, 2026, 280 days later is October 8.
This is a statistical estimate that assumes a 28-day cycle; the actual due date is set by a doctor based on an ultrasound and other checks. Still, this calculation is a great help for getting a feel for counting weeks of pregnancy from dates.

Working back from an exam or event ("days before")

Plans such as "start practice tests 30 days before the exam" or "register by some number of days before the test date" are "days earlier" calculations. If the exam is on November 15, 2026, 30 days before is October 16.
For big events such as a recital, a wedding or a move, turn each "2 weeks before" or "the day before" deadline into a date on your calendar, and nothing will slip through.

Formula

The date \(n\) days later and \(n\) days earlier

Standard notation (the usual math form)

\(D_1\) \(=\) \(D_0\) \(+\) \(n\)

\(D_2\) \(=\) \(D_0\) \(-\) \(n\)

In words (symbols replaced with words)

③ \(D_1\): date \(n\) days later \(=\) ① \(D_0\): start date \(+\) ② \(n\): number of days

\(D_2\): date \(n\) days earlier \(=\) \(D_0\): start date \(-\) \(n\): number of days

The formula in words

① Take the \(D_0\): start date

② add the \(n\): number of days

③ and you get the \(D_1\): date \(n\) days later (subtract instead, and you get the date \(n\) days earlier, \(D_2\))

Quick example

For 10 days after January 15, 2026, add 10 to the day, 15

date 10 days later (January 25) \(=\) start date (January 15) \(+\) number of days (10)

\(15 + 10 = 25\)

Key idea

When you pass the end of a month, carry the days beyond that month's length into the next month. For example, 10 days after January 25, 2026: 25 + 10 = 35, and January has 31 days, so 35 − 31 = 4 gives February 4. Inside computers such as Excel, dates are stored as running numbers with 1 day = 1 (serial numbers), so "date + number of days" is just an addition. The "later" and "earlier" dates in this calculator already carry over into the next month or year.

Turning weeks into days and adding them together

Standard notation (the usual math form)

\(N\) \(=\) \(7\) \(\times\) \(w\) \(+\) \(d\)

In words (symbols replaced with words)

④ \(N\): days to add \(=\) ② \(7\): days in a week \(\times\) ① \(w\): weeks \(+\) ③ \(d\): days

The formula in words

① Take the \(w\): weeks

② multiply by \(7\): days in a week to turn weeks into days

③ add the \(d\): days

④ and you get the \(N\): days to add (then add it to or subtract it from the start date, just as in formula 1)

Quick example

For "3 weeks and 4 days after May 20, 2026", first turn the weeks into days

days to add (25 days) \(=\) days in a week (7) \(\times\) weeks (3 weeks) \(+\) days (4 days)

\(N = 7 \times 3 + 4 = 25\)

Key idea

The rest is the same as formula 1. May has 31 days, so 20 + 25 = 45 and 45 − 31 = 14, and the answer is June 14. Unlike a month, a week is always exactly 7 days, so any number of weeks can be turned into days safely. "2 weeks later" and "14 days later" mean exactly the same thing. The days of the week repeat every 7 days, so adding a multiple of 7 (14 days, 21 days and so on) lands on the same weekday as the start date.

The date some months or years later (same day number)

Standard notation (the usual math form)

\(T\) \(=\) \(12\) \(\times\) \(y\) \(+\) \(m\)

In words (symbols replaced with words)

④ \(T\): total months to add \(=\) ② \(12\): months in a year \(\times\) ① \(y\): years \(+\) ③ \(m\): months

The formula in words

① Take the \(y\): years

② multiply by \(12\): months in a year to turn years into months

③ add the \(m\): months

④ and you get the \(T\): total months to add (move the month \(T\) months ahead and keep the same day number as the start date)

Quick example

For "1 year and 2 months after May 10, 2026", the total months to add is

total months to add (14 months) \(=\) months in a year (12) \(\times\) years (1 year) \(+\) months (2 months)

\(T = 12 \times 1 + 2 = 14\)

Key idea

Moving 14 months ahead gives July 2027, and the day stays 10, the same as the start date, so the answer is July 10, 2027. This "same day number in a later month or year" is called the corresponding date. Be careful when you land in a month that has no such day. For example, 1 month after January 31, 2024 would be "February 31", which does not exist, so it is rounded to the last day of that month (February 29, since 2024 was a leap year). This is why a payday or due date set for the end of the month falls on different days from month to month. When you enter years, months, weeks and days together, this calculator adds them in the order years, then months, then weeks and days. (When month-end rounding happens, this order decides the result.)

The date some business days later (skipping weekends)

Standard notation (the usual math form)

\(C\) \(=\) \(b\) \(+\) \(W\)

In words (symbols replaced with words)

③ \(C\): calendar days to move \(=\) ① \(b\): business days \(+\) ② \(W\): weekend days in between

The formula in words

① Take the \(b\): business days

② add the \(W\): weekend days in between

③ and you get the \(C\): calendar days to move (then move \(C\) days ahead from the start date, just as in formula 1)

Quick example

For 5 business days after Friday, October 2, 2026, there is one Saturday and one Sunday in between, so

calendar days to move (7 days) \(=\) business days (5) \(+\) weekend days in between (2 days)

\(C = 5 + 2 = 7\)

Key idea

Moving 7 days ahead gives the answer: Friday of the next week (October 9, 2026). The number of weekend days \(W\) in between depends on the weekday you start from, so in practice you step forward one day at a time, count only the days that are not Saturday or Sunday, and stop when you reach \(b\) days (this calculator works the same way). Business days in this calculator are "days that are not Saturday or Sunday", and holidays are not skipped. Some federal holidays, such as Thanksgiving (the fourth Thursday of November), fall on a different date every year, and states and companies have their own days off. So when a deadline like "within 5 business days" must skip holidays, check your calendar for holidays in between.

The basics of adding to a date: weeks and days are a simple addition of days, while months and years move you to the same day number (the corresponding date). In a month without that day, round to the end of the month, and when adding everything at once, go in the order years, months, then weeks and days. Business days are counted one day at a time, skipping weekends.

Symbols and terms

Symbols

\(D_0\)	D sub 0	The start date (the date you count from). The small 0 at the lower right is a subscript meaning "number 0 = the starting point".
\(D_1\), \(D_2\)	D sub 1, D sub 2	The resulting dates. \(D_1\) is the date \(n\) days later, and \(D_2\) is the date \(n\) days earlier.
\(n\)	n	The number of days to add or subtract. (Example - for 90 days later, \(n = 90\))
\(w\), \(d\)	w, d	The weeks (\(w\)) and the extra days that do not make a full week (\(d\)). For "3 weeks and 4 days", \(w = 3\) and \(d = 4\).
\(N\)	N (capital)	The weeks and days turned into a single number of days to add. Found with \(N = 7w + d\).
\(y\), \(m\)	y, m	The years (\(y\)) and months (\(m\)) to add or subtract. For "1 year 2 months", \(y = 1\) and \(m = 2\).
\(T\)	T	The years and months turned into a single number of months to add. Found with \(T = 12y + m\).
\(b\)	b	The number of business days (days counted without weekends). From the first letter of "business day".
\(C\), \(W\)	C, W (capital)	When counting business days, the calendar days you actually move (\(C\)) and the weekend days in between (\(W\)). They are related by \(C = b + W\).

Terms

corresponding date	The same day number in a later month or year. For January 15, the corresponding date 1 month later is February 15. "Some months later" and "some years later" are counted with this date. In a month without that day, as with January 31, the last day of that month is used instead.
end-of-month rounding	When the corresponding date does not exist (for example, "February 31" as 1 month after January 31), the last day of that month (February 28 or 29) is used as the answer. This calculator and the Excel EDATE function both work this way.
leap year	A year with a February 29. It usually comes every 4 years, but years divisible by 100 are common years unless they are divisible by 400 (2100 is not a leap year, 2000 was). 1 year after February 29 is February 28, by end-of-month rounding, because the next year has no February 29.
business day	A day when businesses and government offices are open. This calculator counts "days that are not Saturday or Sunday" as business days and does not skip holidays, because federal, state and company holidays differ and some move every year. Contracts may define "business day" in their own way, so check the definition for an official deadline.
serial number	The running number that Excel and other programs use to store dates. January 1, 1900 is 1, and the number goes up by 1 each day. Because a date is really a number, "date + number of days" is just an addition.
31-day month	A month with 31 days (January, March, May, July, August, October, December).
30-day month	A month with 30 days (April, June, September, November). February alone has 28 days (29 in a leap year). The rhyme "Thirty days hath September, April, June and November" is a well-known way to remember them.

Good to know before you start

Here is what helps you use the calculation on this page with real understanding, not just by pressing the button.
If you get stuck, going back over these topics is the quickest way forward.

How the calendar works (Grades 3–4)	Knowing that 1 week = 7 days and 1 year = 12 months Knowing that months have 28 to 31 days (and which months have 31) Knowing that about every 4 years there is a year with a February 29 (a leap year)
Adding and subtracting with regrouping (Grade 2)	Being able to do 2-digit addition and subtraction such as 15 + 10 = 25 and 45 − 31 = 14 Seeing that "carry the days past the end of the month into the next month" is the same idea as regrouping
Multiplication (Grade 3)	Knowing the times tables (such as 7 × 3 = 21) and simple products such as 12 × 2 = 24 Getting the idea of converting units by multiplying, as in turning weeks into days or years into months
Division with remainders and repeating cycles (Grade 4)	Being able to find the quotient and remainder, as in 25 ÷ 7 = 3 remainder 4 Knowing that the days of the week repeat every 7 days (adding a multiple of 7 days brings you back to the same weekday)

How to calculate it in Excel

Copy the whole table below and paste it into cell A1 in Excel. It works as is.

Table for the date n days later and earlier

Start date	2026-01-15
Days n	10
Date n days later	=B1+B2
Date n days earlier	=B1-B2

Table to add weeks and days together

Start date	2026-05-20
Weeks w	3
Days d	4
Days to add N	=B2*7+B3
Date N days later	=B1+B4
Date N days earlier	=B1-B4

Table for the date some years and months later

Start date	2026-05-10
Years y	1
Months m	2
Date y years m months later	=EDATE(B1,B2*12+B3)
Date y years m months earlier	=EDATE(B1,-(B2*12+B3))

Table for the date some business days later (skipping weekends)

Start date	2026-10-02
Business days b	5
Date b business days later	=WORKDAY(B1,B2)
Date b business days earlier	=WORKDAY(B1,-B2)

Table to add years, months, weeks and days together (same as this calculator)

Start date	2026-05-10
Years	1
Months	2
Weeks	3
Days	4
Date after adding all	=EDATE(B1,B212+B3)+B47+B5
Date after subtracting all	=EDATE(B1,-(B212+B3))-B47-B5

Type the start date in the form 2026-01-15 (year-month-day). Excel reads this form as a date whatever your regional settings are. If a result shows up as a 5-digit number such as "46047" (a serial number), change the cell format to "Date".
As the first table shows, adding or subtracting days is just "=date+days" (the answers in the first table are January 25 and January 5). To add or subtract months, use the EDATE function (=EDATE(start date, months)). It even rounds to the end of the month, when the month has no such day, the same way as this calculator. To go back in time, make the number of months negative.
For business days, use the WORKDAY function (=WORKDAY(start date, business days)), which skips weekends (the answer in the fourth table is October 9). If you give a list of holiday dates as the third argument, it skips those holidays too, so use that when holidays matter.
The fifth table matches the inputs of this calculator, and the answer is August 4, 2027. One thing to note: this calculator adds years and then months, while EDATE adds them all at once, so in rare cases involving a leap day (February 29) the results can differ by 1 day (for example, 1 year 1 month after 2024-02-29 is 2025-03-28 in this calculator but 2025-03-29 with =EDATE(B1,13)).

How to calculate it in Google Sheets

Copy the whole table below and paste it into cell A1 in Google Sheets. It works as is.

Table for the date n days later and earlier

Start date	2026-01-15
Days n	10
Date n days later	=B1+B2
Date n days earlier	=B1-B2

Table to add weeks and days together

Start date	2026-05-20
Weeks w	3
Days d	4
Days to add N	=B2*7+B3
Date N days later	=B1+B4
Date N days earlier	=B1-B4

Table for the date some years and months later

Start date	2026-05-10
Years y	1
Months m	2
Date y years m months later	=EDATE(B1,B2*12+B3)
Date y years m months earlier	=EDATE(B1,-(B2*12+B3))

Table for the date some business days later (skipping weekends)

Start date	2026-10-02
Business days b	5
Date b business days later	=WORKDAY(B1,B2)
Date b business days earlier	=WORKDAY(B1,-B2)

Table to add years, months, weeks and days together (same as this calculator)

Start date	2026-05-10
Years	1
Months	2
Weeks	3
Days	4
Date after adding all	=EDATE(B1,B212+B3)+B47+B5
Date after subtracting all	=EDATE(B1,-(B212+B3))-B47-B5

In Google Sheets, EDATE and WORKDAY work exactly as in Excel. Copy the whole table, paste it into cell A1, and replace the dates and numbers in column B with your own.
If a result shows up as a number (a serial number), change it to a date with Format > Number > Date in the menu. As in Excel, EDATE can differ from this calculator by 1 day in rare cases involving a leap day.

How to calculate it in Python

from datetime import date, timedelta
import calendar

start = date(2026, 5, 10)                # start date
years, months, weeks, days = 1, 2, 3, 4  # years, months, weeks and days to add

def add_months(base_date, month_count):
    """Move ahead by months, rounding to the end of the month when that day does not exist (negative goes back)"""
    total_month_index = base_date.year * 12 + (base_date.month - 1) + month_count
    year, month_index = divmod(total_month_index, 12)
    month = month_index + 1
    last_day = calendar.monthrange(year, month)[1]
    return date(year, month, min(base_date.day, last_day))

# Add in the order years, months, then weeks and days (make everything negative to subtract)
after = add_months(add_months(start, years * 12), months) + timedelta(days=weeks * 7 + days)
before = add_months(add_months(start, -years * 12), -months) - timedelta(days=weeks * 7 + days)
print(f"{years} y {months} m {weeks} w {days} d later: {after}")    # 2027-08-04
print(f"{years} y {months} m {weeks} w {days} d earlier: {before}")  # 2025-02-13

def add_business_days(base_date, business_days):
    """Return the date business_days days later, skipping Saturdays and Sundays"""
    current = base_date
    counted = 0
    while counted < business_days:
        current += timedelta(days=1)
        if current.weekday() < 5:  # 0-4 are Monday to Friday
            counted += 1
    return current

print(f"5 business days after 2026-10-02: {add_business_days(date(2026, 10, 2), 5)}")  # 2026-10-09

Runs with the standard library only. Days and weeks can be added or subtracted directly with timedelta (an object for a difference in days), but "1 month" has no fixed length, so timedelta cannot express it. So the add_months function does it by hand: it moves the month number ahead and rounds to the end of the month when that day does not exist (the min(day, last day of the month) part is the month-end rounding). The business day function steps forward one day at a time and counts only the days where weekday() is 0 to 4 (Monday to Friday) - exactly the idea of formula 4.

How to write it in LaTeX and other math languages (copy and paste)

The date \(n\) days later and \(n\) days earlier

D₁ = D₀ + n,  D₂ = D₀ − n

D_1 = D_0 + n, \quad D_2 = D_0 - n

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <msub><mi>D</mi><mn>1</mn></msub><mo>=</mo>
    <msub><mi>D</mi><mn>0</mn></msub><mo>+</mo><mi>n</mi>
    <mo>,</mo><mspace width="0.7em"/>
    <msub><mi>D</mi><mn>2</mn></msub><mo>=</mo>
    <msub><mi>D</mi><mn>0</mn></msub><mo>&#x2212;</mo><mi>n</mi>
  </mrow>
</math>

D_1 = D_0 + n, D_2 = D_0 - n

dateAfter = DatePlus[startDate, n]; dateBefore = DatePlus[startDate, -n]

dateAfter := startDate + n; dateBefore := startDate - n;

date_after = start_date + days(n); date_before = start_date - days(n);

D_1 = D_0 + n, D_2 = D_0 - n

Turning weeks into days and adding them together

N = 7w + d

N = 7w + d

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>N</mi><mo>=</mo>
    <mn>7</mn><mi>w</mi>
    <mo>+</mo><mi>d</mi>
  </mrow>
</math>

N = 7w + d

totalDays = 7*weeks + extraDays

totalDays := 7*weeks + extraDays;

total_days = 7*weeks + extra_days;

N = 7w + d

The date some months or years later (same day number)

T = 12y + m

T = 12y + m

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>T</mi><mo>=</mo>
    <mn>12</mn><mi>y</mi>
    <mo>+</mo><mi>m</mi>
  </mrow>
</math>

T = 12y + m

totalMonths = 12*years + months

totalMonths := 12*years + months;

total_months = 12*years + months;

T = 12y + m

The date some business days later (skipping weekends)

C = b + W

C = b + W

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>C</mi><mo>=</mo>
    <mi>b</mi>
    <mo>+</mo><mi>W</mi>
  </mrow>
</math>

C = b + W

calendarDays = businessDays + weekendDays

calendarDays := businessDays + weekendDays;

calendar_days = business_days + weekend_days;

C = b + W

How to have ChatGPT do the calculation

You are a date calculation assistant. Do the following calculations by actually running Python code, and base your answer only on the dates from the execution result (do not answer by mental math or guessing).

1. The date you get by adding "1 year, 2 months, 3 weeks and 4 days" to May 10, 2026, and the date you get by subtracting it. Add in the order years, then months, then weeks and days. Count "months later" by the same day number in the later month, and if that month has no such day, round to the last day of that month.
2. The date 5 business days after Friday, October 2, 2026. Count business days by skipping only Saturdays and Sundays (do not skip holidays).

For each, show the code you used and the resulting dates and days of the week.

How to Use

1

Enter your numbers

Type the numbers you want to calculate with into the input fields
2

Calculate

Press the "Calculate" button
3

Check the result

The result appears on the spot. The same page also explains the idea behind the calculation and the formula