Add or Subtract Dates Calculator

What date is 30, 60 or 90 days from today?

Count forward on the calendar from today, with tomorrow as day 1. Once the page has loaded, the start date is today’s date on your device and Days holds 90, so the headline already answers “90 days from today”. Type another number in Days, or press 30 days, 60 days or 180 days under the result. Subtract counts back instead.

From a fixed start, Tuesday, October 13, 2026: 30 days later is Thursday, November 12; 60 days later is Saturday, December 12; and 90 days later is Monday, January 11, 2027. “3 months from October 13” is a different question: it lands on Wednesday, January 13, 2027, which is 92 days away, because October and December have 31 days each.

How to add or subtract days, weeks, months or years

• Start date: type the date or pick it from the calendar. The line under the box repeats it with its weekday, which catches a day and month typed the wrong way round. When the page opens, the start date changes from the worked example’s October 13, 2026 to today’s date on your device, and a line under the result says so. Use today’s date puts today back after you change it.
• Add or subtract: Subtract counts back from the start date.
• Years, Months, Weeks and Days: whole numbers from 0 up; a blank box counts as 0. Mix them freely, for example 1 year and 2 weeks. Months can go past 12: the line under the box reads 18 months as 1 year and 6 months. Each box has a ceiling (10,000 years, 120,000 months, 522,000 weeks or 3,653,000 days), and the result must stay between January 1 of the year 1 and December 31, 9999.
• Month-end rule: appears only when the start date is the 29th, 30th or 31st and you move by months or years, the only case where it can change the answer. The sections below explain both choices.
• Count the start date as day 1: for periods that include the day they begin. It moves the result one day toward the start date.

The Try buttons load the three month-end cases worked through below. To compare, press Save for comparison, change something and save again; each later result shows how many days it moves the date.

Years and months first, then weeks and days

The calculator moves by whole months first, counting each year as 12 months, and then adds the weeks (7 days each) and the days. The order only changes the answer when the month step lands near a month end. Press Jan 30 + 1 month and 1 day: January 30, 2027 plus 1 month aims at February 30, which doesn’t exist, so it becomes February 28, and one more day gives Monday, March 1, 2027. Taking the day first would reach January 31 and then February 28, a day earlier. JavaScript’s Temporal date API adds a duration in the same order as this calculator.

Worked example: 90 days after October 13, 2026

A store takes returns within 90 days of purchase, and the purchase was on Tuesday, October 13, 2026. What is the last day to return it?

1. Start and amount: Tuesday, October 13, 2026, add 90 days. No months are added, so no month-end rule is needed.
2. Count through the months: October has 31 days, so 18 remain after the 13th. November adds 30 (48 so far) and December adds 31 (79). The last 90 − 79 = 11 days run into January: January 11, 2027.
3. Check the weekday: 90 days is 12 weeks and 6 days. Whole weeks keep the weekday, and 6 days after a Tuesday is a Monday, so the answer is Monday, January 11, 2027.
4. Day of the year and week: January 11 is day 11 of 365 in 2027. Its ISO week date is 2027-W02-1, the Monday that starts week 2; week 1 of 2027 begins on January 4, because January 1 is a Friday.
5. Spreadsheet check: with October 13, 2026 in cell A1, =A1+90 gives the same date.

Whether the purchase day counts toward the 90 depends on the store’s wording. If it does, tick Count the start date as day 1, and the last day becomes Sunday, January 10, 2027.

The table under the result keeps counting from the purchase date. Because 90 days is not a whole number of weeks, each 90-day mark falls a day earlier in the week than the one before: Monday, January 11; Sunday, April 11; Saturday, July 10, 2027; and so on.

What happens when you add a month to January 31?

There is no February 31, so the answer depends on a rule, and date software doesn’t all use the same one:

Rolling over carries the days February lacks (29, 30 and 31, so 3 days) into March. In a leap year February has a 29th, so January 31, 2028 plus 1 month is February 29, 2028, or March 2, 2028 when rolled over.

Press Jan 31 + 1 month to see both: the result uses the rule you chose and a note under it gives the date under the other one. Subtracting works the same way. March 31, 2027 minus 1 month is February 28 under the last-day rule but Wednesday, March 3 when rolled over, only 28 days back, because the missing days roll forward.

Adding a year to February 29

February 29 exists only in leap years, so a year after it needs the month-end rule too. Press Feb 29 + 1 year: Tuesday, February 29, 2028 plus 1 year is Wednesday, February 28, 2029 with the default rule, 365 days later, or Thursday, March 1, 2029 when rolled over, 366 days later. Four years on, the date exists again: February 29, 2028 plus 4 years is Sunday, February 29, 2032.

A year is a leap year when it divides by 4, except century years, which must divide by 400. So 2000 had a February 29 and 1900 didn’t, and the calculator counts both correctly.

Counting back: what date was it 90 days ago?

Choose Subtract and enter the amount. The steps run in reverse: months back first, then weeks and days back. For example, 90 days before Tuesday, October 13, 2026 was Wednesday, July 15, 2026: the same 12 weeks and 6 days, so the weekday moves 6 days back, from Tuesday to Wednesday.

Does day 1 start today or tomorrow?

By default day 1 is the day after the start date, so 1 day after a Monday is a Tuesday, and 30 days after Saturday, October 3, 2026 is Monday, November 2, 2026. U.S. federal court rules count periods stated in days this way: they leave out the day of the event that starts the period and count the last day.

Some terms count the start date itself, such as “within 30 days, including the day of purchase”. Tick Count the start date as day 1 and the same 30 days end on Sunday, November 1, 2026. Rules also differ on what happens when the last day is a weekend or holiday: the federal court rule, for example, runs on to the next day that isn’t one. This calculator never moves a date for that, so check the rule that applies to your deadline.

Calendar days or business days?

This calculator counts calendar days: every Saturday, Sunday and holiday counts like any other day. For a deadline in working days, use a business days calculator, which skips weekends and the holidays you choose. When the amount is in weeks and days, Continue in the Business Days Calculator under the result carries the start date, the direction and the number of days across, to be counted there as working days.

Adding days or months in Excel and Google Sheets

Put the start date in cell A1 and format the result cell as a date.

• Days: =A1+90 adds 90 days and =A1-90 goes back 90 days. This works because Excel stores dates as serial numbers counted from January 1, 1900.
• Months with the last-day rule: =EDATE(A1,6) adds 6 months and =EDATE(A1,-6) goes back 6. The OpenDocument formula standard defines EDATE to use the last day of the month when the day is missing, like the default rule here.
• Months with the roll-over rule: =DATE(YEAR(A1),MONTH(A1)+6,DAY(A1)). DATE adds a day the month doesn’t have to the first day of that month, so the extra days roll into the next month.
• Months and days together: =EDATE(A1,1)+10 takes the month step first and then the days, in the same order as this calculator.

The steps under the result give the formula for your own numbers. They leave it out for dates before March 1, 1900, because Excel treats 1900 as a leap year for compatibility with an older program, which puts its serial numbers a day off before then.

Day of the year and ISO week numbers

The day of the year counts from January 1 (day 1) to December 31 (day 365, or 366 in a leap year). ISO 8601 week numbers start each week on a Monday, and week 1 is the week that holds the year’s first Thursday. So a few days around New Year belong to the neighboring year’s weeks: Friday, January 1, 2027 falls in week 53 of 2026, written 2026-W53-5, and Monday, December 30, 2024 was in week 1 of 2025. The result gives the whole ISO week date (year, week and weekday, 1 for Monday to 7 for Sunday); in Excel, =ISOWEEKNUM(A1) gives the week number alone.

Reading the result

• The headline is the resulting date with its weekday; the line under it restates the question, such as “90 days after October 13, 2026”.
• The line under the headline says whether the start date is today on your device. Use today’s date and Use the result as the start change the start date without retyping it.
• The month-end note appears when the rule decided the date and gives the date under the other rule.
• Calendar days is the distance from the start date, also in weeks and days. Day of the year and ISO week describe the resulting date.
• From the same start date replaces every amount with a common one (30, 60, 90 or 180 days; 2 or 6 weeks; 3 or 6 months; 1 year) and keeps your start date and direction.
• The steps show the month step, the day step, the day count with a weekday check, and the spreadsheet formula.
• The table repeats the whole step 1 to 12 times, each row counted from the start date: every 3 months, every 90 days and so on. For a step in weeks and days, the note under it says how the weekday moves from row to row. Download it as a CSV file for a schedule of reviews or renewals.
• Continue in passes the dates to the Days Between Dates Calculator, the Countdown to a Date and, for amounts in weeks and days, the Business Days Calculator.

Assumptions and limitations

• Dates are whole calendar days. The time of day, time zones and daylight saving time are not used, so “6 months after” a moment near midnight in another time zone may need adjusting by a day.
• Dates follow the Gregorian calendar, extended back to the year 1, from January 1 of the year 1 to December 31, 9999.
• Weekends and holidays count like any other day, and no date is moved off a weekend.
• The month-end rule is the one you choose. Other tools may use the other rule for the same months, as in the table above, so a second opinion can differ by up to 3 days.
• Which date a contract, a notice period or a court deadline actually ends on is set by its own terms or rules. This calculator does the date arithmetic; it isn’t legal advice.

Common mistakes

• Treating a month as 30 days. Six months after August 31, 2026 is 181 days, and 3 months after October 13, 2026 is 92. When a term is written in months, enter months.
• Leaving an amount in another box. Every box counts, so typing 6 in Months while Days still holds 90 adds 6 months and 90 days. The line under the headline repeats what was added, and the buttons under the result (30 days, 3 months and so on) replace every box at once.
• Adding one month at a time. January 31, 2027 plus 1 month is February 28, and a month after that is March 28; adding 2 months at once gives March 31. The table counts every row from the start date for this reason. Use the result as the start chains the steps on purpose, when that is what you mean.
• Counting from the wrong start. Check that the start date is the one you mean; the line under the headline says whether it is today on your device.
• Counting the start date by habit. Leave Count the start date as day 1 off unless the terms include the first day.
• Typing a two-digit year. A year typed as 26 is the year 26, not 2026. The field points this out; type all four digits.
• Expecting a weekend deadline to move. The result is the plain calendar date, even on a Saturday or Sunday.