Enter a start date and an end date. You get the days between them, the inclusive count (with the end date also counted as a day), and the same period in weeks, months, and years, months and days.
If you leave one date blank, today's date is used. If the start date is after the end date, the two are simply swapped.
Result
Enter a start date and an end date in the fields on the left and press "Calculate". The result will appear here.
Table of Contents
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What you can do on this page
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What is this calculation used for?
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How to Use
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Formula
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Symbols and terms
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Good to know before you start
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How to calculate it in Excel
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How to calculate it in Google Sheets
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How to calculate it in Python
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How to write it in LaTeX and other math languages (copy and paste)
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How to have ChatGPT do the calculation
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DataChef Features
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Related Features
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NumberChef Calculators List
What you can do on this page
- Enter a start date and an end date to get the number of days between them on the spot. Leave one of them blank to count "days until the exam" or "days since our anniversary" from today
- You see both "days between" (the start date not counted) and the inclusive count (both the start and end dates counted), so you will not mix them up when counting hotel nights, days of medicine or prorated rent
- The same period is also shown in years, months and days, in months, and in weeks
- A plain-language explanation of how to count days and copy-and-paste formulas for Excel, Google Sheets and Python are all on this page
Leap days (February 29) are counted correctly, just as on a calendar. This page counts calendar days. It does not count business days (days without weekends and holidays).
What is this calculation used for?
Counting down to an exam or a deadline (study plans)
"If today is July 3 and the exam is on January 16 next year, 197 days are left." Once you know the days left, you can plan with numbers instead of a feeling. For example, to work through 10 practice tests in about 200 days, you have 20 days for each one.
A countdown naturally uses the subtraction, which does not count today. The day before, it shows "1 day left", and on the day itself, "0 days left".
Not mixing up nights and days on a trip
A trip where you check in on August 13 and check out on August 16 is \(16 - 13 = 3\) nights by subtraction, and 4 days by the inclusive count - "3 nights, 4 days".
Hotels charge by the night (subtraction), while things like travel insurance and some rentals charge by the day (inclusive count). Knowing the difference keeps your budget right. (Car rentals often charge per 24 hours rather than per calendar day.)
Counting days of medicine and prescription refills (health)
A 7-day supply of medicine that starts on July 1 is counted inclusively, so the last day you take it is July 7. If you think of it as a subtraction (\(7 - 1 = 6\)), you are off by one day.
Checking "will my medicine last until my next appointment or refill?" means comparing two counts that work differently: the days supplied (inclusive count) and the days until the appointment (subtraction). Knowing the difference helps you avoid running out.
Prorating rent and pay (money)
If you move in on July 10, the first month's rent is often prorated for 22 days out of 31 (inclusive count, \(31 - 10 + 1 = 22\)). You use the apartment on the move-in day itself, so the first day is counted.
Pay for starting or leaving a job in the middle of a month works the same way. How days are counted (inclusive or not) can depend on the lease or contract, so use this to check the numbers against what your contract says.
Counting days of interest on savings and loans (counting one end)
Interest is calculated in proportion to the number of days, as in "principal × rate × days ÷ 365". Banks commonly count interest from the day of the deposit up to, but not including, the day of the withdrawal - that is, counting one end only, the same as the subtraction.
For example, if you deposit money on April 1 and withdraw it on April 30, that is 29 days of interest. A one-day difference in counting changes the interest, so this helps you read the day-count terms in your account or loan documents.
Counting weeks of pregnancy and the due date (splitting into weeks)
Pregnancy is counted from the first day of the last menstrual period as day 0, and day 280 (\(280 = 7 \times 40\), so 40 weeks 0 days) is the usual estimated due date. "How many weeks and days pregnant am I today?" is exactly the weeks formula on this page: divide the days since the start date by 7.
Prenatal visits and tests are scheduled by week, so being able to switch between days and weeks makes your records much easier to follow.
Formula
Days between two dates (by subtraction)
Standard notation
(the usual math form)
\(D\)
\(=\)
\(N_2\)
\(-\)
\(N_1\)
In words
(symbols replaced with words)
③
\(D\): days between the dates
\(=\)
①
\(N_2\): serial number of the end date
\(-\)
②
\(N_1\): serial number of the start date
The formula in words
①
Take the
\(N_2\): serial number of the end date
②
subtract the
\(N_1\): serial number of the start date
③
and you get the
\(D\): days between the dates
(counting the start date as day 0)
Quick example
The number of days from January 1, 2025 to March 1, 2025 is (using the same serial numbers as Excel, where January 1, 1900 is number 1, January 1, 2025 is 45658 and March 1, 2025 is 45717)
\(D\): days between the dates
\(=\)
serial number of the end date (45717)
\(-\)
serial number of the start date (45658)
\(45717 - 45658 = 59\)
Key idea
A "serial number" is a number given to every date on the calendar in order, one per day (Excel calls it a serial number too). With subtraction, you get an exact count without worrying about the different month lengths (28 to 31 days) or leap years.
To count by hand, go month by month and add. January 1 to January 31 is \(31 - 1 = 30\) days, February has 28 days, and 1 more day brings you to March 1, so \(30 + 28 + 1 = 59\) days.
Note that this formula does not count the start date (it counts the start date as day 0). From January 1 to January 2 is 1 day.
Counting the end date too (inclusive count)
Standard notation
(the usual math form)
\(D'\)
\(=\)
\(D\)
\(+\)
\(1\)
In words
(symbols replaced with words)
③
\(D'\): inclusive count
\(=\)
①
\(D\): days between the dates
\(+\)
②
\(1\): the start date itself
The formula in words
①
Take the
\(D\): days between the dates
②
add
\(1\): the start date itself
③
and you get the
\(D'\): inclusive count
(both the start date and the end date count as a day)
Quick example
From January 1, 2025 to March 1, 2025, counting both the first and the last day, gives
\(D'\): inclusive count
\(=\)
days between the dates (59 days)
\(+\)
the start date itself (1 day)
\(59 + 1 = 60\)
Key idea
The days \(D\) from subtraction do not count the start date. This is what you want for a countdown such as "days until the exam", or for the number of nights in a hotel.
On the other hand, when both the first and the last day should count, such as the days you take a medicine, the days of a rental, or "how many days does the festival run", add 1 to get the inclusive count. The most important step in counting days is to decide first which of the two counts the situation needs.
Days in weeks
Standard notation
(the usual math form)
\(D\)
\(=\)
\(7\)
\(\times\)
\(W\)
\(+\)
\(r\)
In words
(symbols replaced with words)
①
\(D\): days between the dates
\(=\)
②
\(7\): days in a week
\(\times\)
③
\(W\): weeks
\(+\)
④
\(r\): extra days
The formula in words
①
Divide the
\(D\): days between the dates
②
by
\(7\): days in a week
③
the whole-number answer is the
\(W\): weeks
④
and the remainder is the
\(r\): extra days
Quick example
59 days in weeks is (\(59 \div 7 = 8\) remainder \(3\), so "8 weeks and 3 days")
days between the dates (59 days)
\(=\)
days in a week (7)
\(\times\)
weeks (8 weeks)
\(+\)
extra days (3 days)
\(59 = 7 \times 8 + 3\)
Key idea
Turning days into weeks is simply division by 7 with a remainder. The whole-number answer is the weeks, and the remainder is the extra days.
Pregnancy written as "X weeks Y days" and a baby's age in weeks are counted the same way.
Days in years, months and days, and in months
Standard notation
(the usual math form)
\(M\)
\(=\)
\(12\)
\(\times\)
\(y\)
\(+\)
\(m\)
In words
(symbols replaced with words)
④
\(M\): total months
\(=\)
②
\(12\): months in a year
\(\times\)
①
\(y\): years
\(+\)
③
\(m\): extra months
The formula in words
①
Split the period into "\(y\) years \(m\) months \(d\) days" and take the
\(y\): years
②
multiply by
\(12\): months in a year
to turn years into months
③
add the
\(m\): extra months
④
and you get the
\(M\): total months
(the extra days \(d\) cannot become months because months are not all the same length, so they stay as days)
Quick example
April 10, 2024 to June 20, 2025 (= 1 year, 2 months and 10 days) in months is
\(M\): total months
\(=\)
months in a year (12)
\(\times\)
years (1 year)
\(+\)
extra months (2 months)
\(12 \times 1 + 2 = 14\)
Key idea
The answer in this example is "14 months and 10 days". The split into "1 year, 2 months, 10 days" follows the calendar, the same way as an age: starting from the start date, first add as many whole years as fit (1 year), then whole months (2 months), and count what is left in days (10 days).
A month is counted as complete when you reach the same day number in the next month (the corresponding date). The different month lengths (28 to 31 days) are built into this count, so there is no fixed rule such as "1 month = 30 days". For what happens when the next month has no such day, as with January 31, see "corresponding date" in the glossary.
Counting days starts with subtracting one date from the other, which gives the days without counting the start date. When both the first and the last day should count, add 1 (the inclusive count). The trick is to decide first which of the two counts you need.
Symbols and terms
Symbols
| \(D\) | D | The number of days between two dates (the answer of the date subtraction, with the start date as day 0). From the first letter of "days". |
| \(N_1\), \(N_2\) | N sub 1, N sub 2 | The serial numbers of the start date (\(N_1\)) and the end date (\(N_2\)). The same idea as the serial numbers in Excel, which count days with January 1, 1900 as number 1. |
| \(D'\) | D prime | The inclusive count, with both the start date and the end date counted as a day. \(D' = D + 1\). The prime mark (′) is often used for a slightly changed version of the original quantity. |
| \(W\), \(r\) | W, r | The weeks (\(W\)) and the extra days (\(r\)). Divide the days \(D\) by 7. The whole-number answer is \(W\) and the remainder is \(r\). |
| \(y\), \(m\), \(d\) | y, m, d (lowercase) | The parts of a period split into "\(y\) years \(m\) months \(d\) days". (Example - for 1 year, 2 months and 10 days, \(y = 1\), \(m = 2\), \(d = 10\)) |
| \(M\) | M (capital) | The period written in months only (total months). Found with \(M = 12y + m\). (Example - 1 year 2 months is \(M = 14\) months) |
Terms
| calendar days | Every day on the calendar, counted the same whether it is a weekday, a weekend or a holiday. This is different from business days (days without weekends and holidays). This page counts calendar days. |
| exclusive count | A way of counting a period that does not count the first day. Subtracting one date from the other gives this count, with the start date as day 0. "Within 3 days from today" in this sense starts counting from tomorrow. Many legal and contract deadlines are counted this way, but check the exact wording when it matters. |
| inclusive count | A way of counting in which both the start date and the end date count as a day. It is the answer of the date subtraction plus 1. It is used when each day itself is used, such as days of medicine, rental periods or the length of a construction job. |
| counting one end | A way of counting in which only one of the start date and the end date is counted. The answer is the same as the date subtraction. Banks often count interest days this way - interest is earned from the day of the deposit up to, but not including, the day of the withdrawal. If neither end is counted, the answer is the subtraction minus 1. |
| corresponding date | The same day number in a later month or year. For January 15, the corresponding date in the next month is February 15. The extra months in a period are counted by whether this date has been reached. When the next month has no such day, as with January 31, the last day of that month takes its place, and the month is complete when that last day ends. |
| 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). This calculator counts like a calendar, so a February 29 inside the period is counted as a day. |
| serial number | The running number that Excel and spreadsheets use to store dates. January 1, 1900 is 1, and the number goes up by 1 each day (January 1, 2025 is 45658). You can subtract one date from another in Excel because a date is really this number. Excel has an old quirk of counting a "February 29, 1900" that never existed, so these numbers are 1 larger than a true calendar count (this does not affect the number of days you get by subtraction). |
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) |
|
| Subtraction on paper (Grades 2–4) |
|
| Division with remainders (Grade 4) |
|
| Multi-digit multiplication (Grades 4–5) |
|
How to calculate it in Excel
Copy the whole table below and paste it into cell A1 in Excel. It works as is.
Table to find the days between two dates
| Start date | 2025-01-01 |
| End date | 2025-03-01 |
| Days between (start date not counted) | =B2-B1 |
| Inclusive count (both dates counted) | =B2-B1+1 |
Table for the days in weeks
| Start date | 2025-01-01 |
| End date | 2025-03-01 |
| Weeks | =INT((B2-B1)/7) |
| Extra days | =MOD(B2-B1,7) |
Table for years, months and days, and total months
| Start date | 2025-01-01 |
| End date | 2025-03-01 |
| Years | =DATEDIF(B1,B2,"Y") |
| Extra months | =DATEDIF(B1,B2,"YM") |
| Extra days | =DATEDIF(B1,B2,"MD") |
| Total months | =DATEDIF(B1,B2,"M") |
Table for days since and until today (a trick that needs no second date)
| A past date (such as an anniversary) | 2025-01-01 |
| Days from that date to today | =TODAY()-B1 |
| A future date (such as an exam) | 2027-01-16 |
| Days from today to that date (days left) | =B3-TODAY() |
Type dates in the form 2025-01-01 (year-month-day). Excel reads this form as a date whatever your regional settings are. You can subtract one date from another directly: in the first table, B3 shows 59 and B4 shows 60. The second table gives 8 weeks and 3 extra days, and the third gives 0 years, 2 extra months, 0 extra days and 2 total months. If "=B2-B1" shows up as a date such as "2/28/1900", change the cell format to "Number".
In the DATEDIF function in the third table, the third argument means: "Y" = years, "YM" = extra months, "MD" = extra days, "M" = total months. (DATEDIF does not appear in the list of suggested functions, but it has worked in every version of Excel.) However, "MD" is known to be off by 1 or 2 days, or even to give odd values, around the ends of months (for example, when you start on the 31st). When the extra days matter, use this calculator's result as your guide.
With TODAY() as in the fourth table, the "since today" and "until today" counts update every time you open the file.
In the DATEDIF function in the third table, the third argument means: "Y" = years, "YM" = extra months, "MD" = extra days, "M" = total months. (DATEDIF does not appear in the list of suggested functions, but it has worked in every version of Excel.) However, "MD" is known to be off by 1 or 2 days, or even to give odd values, around the ends of months (for example, when you start on the 31st). When the extra days matter, use this calculator's result as your guide.
With TODAY() as in the fourth table, the "since today" and "until today" counts update every time you open the file.
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 to find the days between two dates
| Start date | 2025-01-01 |
| End date | 2025-03-01 |
| Days between (start date not counted) | =B2-B1 |
| Inclusive count (both dates counted) | =B2-B1+1 |
Table for the days in weeks
| Start date | 2025-01-01 |
| End date | 2025-03-01 |
| Weeks | =INT((B2-B1)/7) |
| Extra days | =MOD(B2-B1,7) |
Table for years, months and days, and total months
| Start date | 2025-01-01 |
| End date | 2025-03-01 |
| Years | =DATEDIF(B1,B2,"Y") |
| Extra months | =DATEDIF(B1,B2,"YM") |
| Extra days | =DATEDIF(B1,B2,"MD") |
| Total months | =DATEDIF(B1,B2,"M") |
Table for days since and until today (a trick that needs no second date)
| A past date (such as an anniversary) | 2025-01-01 |
| Days from that date to today | =TODAY()-B1 |
| A future date (such as an exam) | 2027-01-16 |
| Days from today to that date (days left) | =B3-TODAY() |
In Google Sheets, DATEDIF, TODAY, INT and MOD work exactly as in Excel. Copy the whole table, paste it into cell A1, and replace the dates in B1 and B2 with your own.
As in Excel, if a subtraction shows up as a date, change the format to "Number" (Format > Number), and DATEDIF with "MD" can be off by 1 or 2 days around the ends of months.
As in Excel, if a subtraction shows up as a date, change the format to "Number" (Format > Number), and DATEDIF with "MD" can be off by 1 or 2 days around the ends of months.
How to calculate it in Python
from datetime import date
start = date(2025, 1, 1) # start date
end = date(2025, 3, 1) # end date (use date.today() for today)
days = (end - start).days # days between the two dates (start date not counted)
days_inclusive = days + 1 # counting both the start and end dates (inclusive)
weeks, extra_days = divmod(days, 7) # weeks and extra days
# Total months: year difference x 12 + month difference. If the end day comes before the start day, the last month is not complete yet, so subtract 1
total_months = (end.year - start.year) * 12 + (end.month - start.month) - (end.day < start.day)
print(f"Days: {days} days ({days_inclusive} days inclusive)")
print(f"Weeks: {weeks} weeks and {extra_days} days")
print(f"Total months: {total_months} months")
Runs with the standard library only. You can subtract one date from another directly, and ".days" gives the number of days as a whole number. In the total months line, "(end.day < start.day)" checks whether the day of the end date comes before the day of the start date, which means the last month is not complete yet. Python treats the result True/False as 1/0 in subtraction (the same idea as the adjustment in the age formula).
How to write it in LaTeX and other math languages (copy and paste)
Days between two dates (by subtraction)
D = N₂ − N₁
D = N_2 - N_1
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mrow>
<mi>D</mi><mo>=</mo>
<msub><mi>N</mi><mn>2</mn></msub><mo>−</mo>
<msub><mi>N</mi><mn>1</mn></msub>
</mrow>
</math>
D = N_2 - N_1
days = DateDifference[startDate, endDate, "Day"]
days := n2 - n1;
days_between = days(end_date - start_date);
D = N_2 - N_1
Counting the end date too (inclusive count)
D′ = D + 1
D' = D + 1
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mrow>
<msup><mi>D</mi><mo>′</mo></msup><mo>=</mo>
<mi>D</mi><mo>+</mo><mn>1</mn>
</mrow>
</math>
D' = D + 1
daysInclusive = days + 1
daysInclusive := days + 1;
days_inclusive = days_between + 1;
D' = D + 1
Days in weeks
D = 7W + r (0 ≤ r ≤ 6)
D = 7W + r\ \ (0 \le r \le 6)
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mrow>
<mi>D</mi><mo>=</mo>
<mn>7</mn><mi>W</mi><mo>+</mo><mi>r</mi><mspace width="0.7em"/>
<mo>(</mo><mn>0</mn><mo>≤</mo><mi>r</mi><mo>≤</mo><mn>6</mn><mo>)</mo>
</mrow>
</math>
D = 7W + r (0 <= r <= 6)
{weeks, remDays} = QuotientRemainder[days, 7]
weeks := iquo(days, 7); remDays := irem(days, 7);
num_weeks = floor(days_between/7); rem_days = mod(days_between, 7);
D = 7W + r (0 ≤ r ≤ 6)
Days in years, months and days, and in months
M = 12y + m
M = 12y + m
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<mrow>
<mi>M</mi><mo>=</mo>
<mn>12</mn><mi>y</mi>
<mo>+</mo><mi>m</mi>
</mrow>
</math>
M = 12y + m
totalMonths = 12*years + extraMonths
totalMonths := 12*years + extraMonths;
total_months = 12*num_years + extra_months;
M = 12y + m
How to have ChatGPT do the calculation
You are a day-counting assistant. Do the following calculation by actually running Python code, and base your answer only on the numbers from the execution result (do not answer by mental math or guessing). The start date is January 1, 2025, and the end date is March 1, 2025. Find each of the following: 1. The number of days between the two dates (the date subtraction, with the start date as day 0) 2. The number of days counting both the start date and the end date as a day (inclusive count) 3. The number from 1 written as "X weeks and Y days" Show the code you used and the numbers from the execution result.
How to Use
-
1Enter your numbersType the numbers you want to calculate with into the input fields
-
2CalculatePress the "Calculate" button
-
3Check the resultThe result appears on the spot. The same page also explains the idea behind the calculation and the formula
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