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Date Calculator.
Two jobs: count the days between two dates, or land on the date a certain time from now. Both the way a calendar does it.
Results are computed in your browser from the numbers you enter; nothing is sent to us. Double-check anything you rely on. Terms.
Guide
How to use the Date Calculator
There are two modes. Days between two dates answers "how long from here to there?" Add or subtract from a date answers "what date is 90 days from now?" Pick the tab that matches your question.
- For a span between dates, choose Days between two dates and enter the Start date and the End date. Put the earlier date first; if you don't, the calculator swaps them and tells you.
- Decide whether to check Include the end day in the count. Unchecked, the calculator counts the nights between the two dates, the way a hotel or a loan does. Checked, it counts both the first and last day, the way a vacation or rental period usually does.
- Read the results: the Days between headline, Weeks and days, and Business days (Mon–Fri), which counts Mondays through Fridays and does not remove holidays.
- For a date in the future or past, switch to Add or subtract from a date. Enter the Start date, then set Direction to Add or Subtract.
- Fill in any combination of Years, Months, Weeks and Days, leaving the ones you do not need at zero.
- Read the Resulting date and its weekday. The weekday is the part people usually need and forget to check.
How the math works
Counting days is subtraction on the calendar, done exactly, with every 28, 29, 30 and 31-day month at its true length. Weeks are the day count divided by 7, with the remainder shown as extra days. Business days are found by walking from the start to the end and counting each weekday.
Adding happens in two stages. Years and months go first, by calendar: the month number moves and the day of the month stays put, and if that day does not exist in the target month (the 31st in a 30-day month), the date snaps to the month's last day. Weeks and days are added after that, as an exact number of days. Subtracting works the same way in reverse.
The formula
Total days = End date − Start date (+ 1 if Include the end day in the count is checked)
Weeks = Total days ÷ 7, rounded down ; leftover Days = Total days − Weeks × 7
Business days = the number of Mondays through Fridays in the span
Result date = Start date + Years and Months (by calendar, day clamped to the month's last day) + Weeks × 7 + Days
Worked example
Mode A, days between two dates: Start date October 27, 2026, End date April 15, 2027, with Include the end day in the count unchecked.
| Output | How it is counted | Result |
|---|---|---|
| Total days | Exact calendar count from October 27 to April 15 | 170 days |
| Weeks + days | 170 ÷ 7 = 24 weeks, remainder 2 | 24 weeks 2 days |
| Business days | 24 full weeks × 5 = 120, plus the leftover Tuesday and Wednesday | 122 business days |
Check Include the end day in the count and every number shifts by one: 171 days and 123 business days, because April 15, 2027 is a Thursday and it now counts.
Mode B, adding to a date: Start date October 27, 2026, Direction set to Add, 90 in Days. The calculator walks through the rest of October (4 days), November (30) and December (31), which uses up 65 days, then 25 more into January. The result is January 25, 2027, a Monday. That is not the same as adding 3 months, which lands on January 27; a "quarter" measured in months runs anywhere from 89 to 92 days depending on where you start.
And the snap-to-month-end case: January 31, 2027 plus 1 month. February 2027 has 28 days, so there is no February 31, and the calculator returns February 28, 2027, a Sunday. Add 2 months instead and you get March 31, because March has a 31st. The clamp applies only to the month you land in.
Where date math goes wrong
Fencepost errors
The most common mistake is being off by one. Monday to Friday is 4 days apart but 5 days long. For nights (hotel, car rental, loan interest), leave Include the end day in the count unchecked; for days of coverage, leave, or work, check it.
Both answers are "correct" for different questions, so decide which one you mean before you read the number.
Business days are not working days
The business-day count treats every Monday through Friday as a working day. It does not know about Thanksgiving, Christmas, your company's shutdown week, or bank holidays that fall on a Monday, so for a deadline that excludes holidays, subtract them yourself. "10 business days" from Tuesday, October 27, 2026 lands on Tuesday, November 10 by this count, and any holiday in between pushes it later.
"A month from now" is not fixed
Thirty days, one month, and four weeks are three different things. From January 31, 2027, one month is February 28, thirty days is March 2, and 31 days is March 3. Contracts and billing cycles usually say which one they mean; if yours does not, ask before you assume.
Order of operations
Years and months are applied before weeks and days: calendar units first, then fixed-length units. Adding the pieces in another order can shift the result by a day or two, so if a contract spells out its own order, follow the contract.
Everyday uses
Net-30 invoice terms: October 27, 2026 plus 30 days is Thursday, November 26, 2026, which is the fourth Thursday of November, Thanksgiving in the United States, so expect the payment on the next business day. A two-week notice given Tuesday, October 27 ends Tuesday, November 10. Ninety-day probation that starts October 27 ends January 25. Subtract 90 days from October 27, 2026 and you get Wednesday, July 29, 2026, which is how you find a cutoff like "within the last 90 days."
When you need someone's age rather than a plain gap between dates, the Age Calculator breaks the span into years, months and days and tells you the next birthday. For loan payoff dates, the Loan Calculator and the Amortization Calculator figure the end date from the payment count.
What this calculator doesn't do
It does not exclude holidays from business days and does not know your organization's calendar; it counts Monday through Friday, period. It works in whole days, with no time-of-day or time-zone component, so a span that starts at 11 p.m. and ends at 1 a.m. is still counted as the calendar dates say.
It uses the Gregorian calendar only, and it applies no legal rule about deadlines that fall on a weekend. If a result lands on a Saturday or Sunday, you decide whether it moves earlier or later.
Frequently asked questions
How do I count the number of days between two dates?
Subtract the start date from the end date using the actual calendar, so every month is counted at its true length. From October 27, 2026 to April 15, 2027 is 170 days, which is 24 weeks and 2 days. Check the Include the end day in the count box if you want both the first and last day counted.
What counts as a business day?
Any Monday through Friday. The calculator does not remove public holidays or company closures, so for a deadline that excludes holidays you need to subtract them yourself. October 27, 2026 to April 15, 2027 contains 122 business days.
What date is 90 days from today?
Add 90 calendar days to today's date. From October 27, 2026, 90 days later is Monday, January 25, 2027. That is not the same as 3 months, which would land on January 27, because months vary in length.
What happens when I add a month to the 31st?
The calculator adds months by calendar and, if the day does not exist in the new month, snaps to that month's last day. January 31, 2027 plus 1 month is February 28, 2027, since February 2027 has only 28 days.
Should I include the end date when counting days?
It depends on what you are counting. Nights of a hotel stay, days of loan interest, and gaps between events do not include the end day; days of vacation, leave, or coverage usually do. The two answers always differ by exactly one day.
Is a month the same as 30 days or 4 weeks?
No. A calendar month runs 28 to 31 days, 4 weeks is exactly 28 days, and 30 days is 30 days. From January 31, 2027, one month is February 28 while 30 days is March 2, so check which one your contract or billing cycle actually means.
Results are computed in your browser from the numbers you enter; nothing is sent to us. Double-check anything you rely on. See the terms of use.
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