Time & Date · Updated 2026

Date Calculator

Add or subtract days, weeks, months, and years from any date. Find what date it will be in X days, or how long until a future date. Two modes: add/subtract, or find the difference.

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Add or Subtract
Days, Weeks, Months, Years
Business Days Option
Date Difference Mode
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Date Calculator
Add, subtract, or find the difference
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Enter a date and an amount to add or subtract.

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Adding and Subtracting Dates

Adding days is plain calendar counting: September 21, 2026 plus 90 days is Sunday, December 20, 2026. Months and years are added as calendar units, so January 31 plus one month is February 28, 2026. The calculator above adds or subtracts any mix of years, months, weeks and days, and its second tab finds the exact gap between two dates.

Adding Months: the End-of-Month Rule

A month has no fixed length, so the calculator moves the month number and keeps the day. When that day does not exist in the target month, it uses the last day of the month instead.

Start dateChangeResult
Jan 31, 2026plus 1 monthFeb 28, 2026
Jan 31, 2028plus 1 monthFeb 29, 2028 (leap year)
Jan 31, 2026plus 2 monthsMar 31, 2026
Mar 31, 2026plus 1 monthApr 30, 2026
Aug 31, 2026plus 6 monthsFeb 28, 2027
Feb 29, 2028plus 1 yearFeb 28, 2029
Mar 31, 2026minus 1 monthFeb 28, 2026

Months are always counted from the original date, which is why January 31 plus 2 months is March 31 and not March 28. Years and months are applied first, then weeks and days.

90 Days or 3 Months? Why Results Differ

Three calendar months can be anywhere from 89 to 92 days long, so "90 days" and "3 months" only sometimes land on the same date.

Start datePlus 90 daysPlus 3 monthsDays in those 3 months
Jan 15, 2026Apr 15, 2026Apr 15, 202690
Jun 1, 2026Aug 30, 2026Sep 1, 202692
Nov 30, 2026Feb 28, 2027Feb 28, 202790
Dec 1, 2027Feb 29, 2028Mar 1, 202891

The same thing happens with weeks and business days. Starting from Saturday, January 31, 2026: plus 30 days is Monday, March 2; plus 4 weeks is Saturday, February 28; plus 1 month is also February 28; and plus 20 business days is Friday, February 27.

Counting Deadlines Correctly

The start date is day zero

The calculator does not count the start date, so Monday plus 1 day is Tuesday. Federal courts count the same way: Rule 6(a) of the Federal Rules of Civil Procedure excludes the day of the event that starts the period, counts every day after it including weekends and holidays, and includes the last day.

Weekends and holidays at the end

Many rules push a deadline that lands on a weekend or legal holiday to the next business day. Federal court deadlines work that way, and the IRS treats a return or payment as on time when the due date falls on a Saturday, Sunday or legal holiday and you file on the next business day. The calculator shows the plain date, so check the weekday in the result and move it yourself when your rule says so.

Business days skip weekends only

The "Business days only" option skips Saturdays and Sundays. For deadlines that also skip federal holidays, use the business days calculator, and for a plain count of days between two dates try days between dates.

Method and sources. Dates are added on the Gregorian calendar using your device's local date. Years and months are added as calendar units counted from the start date, and a day that does not exist in the target month becomes the last day of that month; weeks and days are then added one calendar day at a time. Every example on this page was computed with the same method. Deadline rules: Federal Rules of Civil Procedure, Rule 6(a) (uscourts.gov); IRS guidance on due dates that fall on a weekend or legal holiday.
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Date Calculator Questions

To find what date is 30 days from today, set Start Date to today, leave direction as "Add," enter 30 in the Days field, and click Calculate. The result depends on the current date: if today is May 15, 2026, then 30 days later is June 14, 2026. The calculator accounts for the varying number of days in each month and leap years automatically. Use the "Today" quick button to set the start date without typing.

Enter your start date, select "Add," then enter the number of months in the Months field. Adding months is not the same as adding 30 days per month: this calculator adds true calendar months. For example, adding 1 month to January 31 gives February 28 (or 29 in a leap year), because February has fewer days. Similarly, adding 1 month to March 31 gives April 30. This is the correct behavior for contract deadlines, subscription renewals, and billing cycles.

Calendar days include every day of the week, including Saturdays and Sundays. Business days count only Monday through Friday. If you select "Business days only," the calculator skips weekends when counting. Example: adding 10 business days to a Monday gives the Monday two weeks later (skipping 4 weekend days). This is useful for calculating shipping deadlines, legal notice periods, payment terms, and HR processes where weekends are excluded. Public holidays are not excluded here; the business days calculator can also skip US federal holidays.

Set Start Date to today, change direction to "Subtract," enter 90 in the Days field, and click Calculate. The result is the date 90 days before today. This is useful for calculating lookback periods, financial reporting windows, statute of limitations checks, and return or refund windows. You can also combine units: for example, subtract 3 months instead of 90 days to get the same month three calendar months back (which differs slightly due to month lengths).

When you add years to a date, the calculator adds true calendar years. If the original date is February 29 (a leap day) and you add 1 year to reach a non-leap year, the result becomes February 28. Adding 4 years to February 29 normally lands on February 29 again, because the year four later is also a leap year (a jump across a century year such as 2100 is the exception). February 29, 2000 + 1 year = February 28, 2001. February 29, 2000 + 4 years = February 29, 2004 (if 2004 is a leap year, which it is). Edge cases like these are handled correctly by this calculator.

A fiscal year (FY) is a 12-month accounting period that may or may not align with the calendar year. US federal government: October 1 to September 30. UK personal tax year: April 6 to April 5. Many corporations use their own FY start. To find the end of a fiscal year, enter the FY start date and add exactly 1 year, then subtract 1 day. Example: FY starting April 6, 2025 ends April 5, 2026. To find what quarter a date falls in, calculate the number of months since the FY start and divide by 3.

Enter the date the contract starts or notice is given as Start Date. Add the required period (e.g., 30 days, 3 months, 1 year). For legal deadlines, always clarify whether the period is in calendar days, business days, or calendar months: the result differs. Example: a 30-day notice starting February 1 ends March 3 (calendar days) or, in 2026, March 13 (business days, skipping weekends). For critical legal matters, verify with a solicitor or attorney, as some jurisdictions exclude the first day, last day, or both from the count.

Switch to the "Date Difference" tab, set Start Date to today, and set End Date to December 25 (Christmas) or December 31 (New Year's Eve). The result shows the exact number of days, and dividing by 7 gives the weeks. For even easier use, click "Today" for the start date and "Dec 31" for the end date to get the days remaining in the current year in one click. This works for any recurring annual date: just enter the upcoming date as the End Date.

ISO 8601 is the international standard for dates and times, using the format YYYY-MM-DD (year-month-day). Example: May 15, 2026 = 2026-05-15. This format is unambiguous across cultures: unlike 05/06/2026 which means June 5 in the US but May 6 in Europe. ISO 8601 sorts chronologically when sorted alphabetically, making it ideal for filenames and databases. The HTML date input in this calculator uses ISO 8601 format internally. Times extend to YYYY-MM-DDTHH:MM:SS, and durations use P1Y2M3D (1 year, 2 months, 3 days).

Use the Date Difference tab: enter the birth date as Start Date and today as End Date. The result shows the total days, weeks, and months. Divide total days by 365.25 for age in decimal years, or use the Months figure divided by 12. For a dedicated age calculator with years, months, and days clearly broken out, visit our Age Calculator page. To find the exact date when someone turns a specific age, use the Add/Subtract tab: enter the birth date and add the number of years of the desired age.

Not usually. Three calendar months last 89 to 92 days depending on which months they cover. From June 1, 2026, 90 days later is August 30, while 3 months later is September 1. A contract or lease that says "3 months" means calendar months; one that says "90 days" means exactly 90 calendar days.

No. The start date is day zero, so adding 1 day to a Monday gives Tuesday. That matches how most US deadlines are counted, including federal court deadlines, which exclude the day of the event that starts the clock. If your rule counts the start date as day 1, enter one day fewer.
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