Date calculator

Find the date a number of days, weeks, months or years before or after another date. Switch to business days to skip weekends and holidays.

By the Calcist team · Checked against known answers · Updated October 27, 2026

Private: calculated on your device. Nothing you type is sent anywhere.

Next: Need the gap between two dates you already know? Try days between dates, or check the weekday with the day of the week calculator.

How the date is worked out

Years and months are added first, then weeks and days:

1. Move the month: month + (years × 12 + months)
2. Keep the same day number, or use the month's last day if it's shorter
3. Add weeks × 7 + days on the calendar

Days are counted on the calendar, so a daylight saving change never makes the answer a day off.

The month-end rule

What is January 31 plus one month? February has no 31st, so the answer is the last day of February: February 28, or February 29 in a leap year. The same happens with March 31 minus one month, or August 31 plus one month (September 30). Spreadsheets like Excel's EDATE use the same rule.

Because of this, adding one month and then subtracting one month doesn't always get you back where you started: January 31 + 1 month = February 28, and February 28 − 1 month = January 28.

Worked examples

90 days from October 27, 2026: 5 days left in October, then 30 in November and 31 in December make 66, and 24 more in January lands on January 25, 2027.
January 31, 2024 + 1 month: 2024 is a leap year, so it's February 29, 2024.
5 business days after Friday, November 20, 2026, skipping holidays: Mon 23, Tue 24, Wed 25, (Thanksgiving Thursday 26 skipped), Fri 27, Mon 30. The answer is November 30, 2026.

Business days

A business day here is Monday to Friday. The start date itself is never counted: 1 business day after a Friday is the next Monday. With holidays on, the 11 US federal holidays are skipped on the days they're observed (a Saturday holiday is observed the Friday before, a Sunday holiday the Monday after).

Limitations

Legal and court deadlines often have their own counting rules (for example, what happens when the last day is a weekend). Follow the rule for your case.
State and company holidays, like the day after Thanksgiving, aren't included. Banks also close on federal holidays but some businesses don't.
Holidays are only skipped from 1971, when today's Monday holiday rules began.

Sources

U.S. Naval Observatory: Introduction to calendars (Gregorian leap-year rule)
U.S. Office of Personnel Management: Federal holidays (dates and the Saturday/Sunday "observed" rule)
5 U.S. Code § 6103 (the list of legal public holidays)

How we checked this

Before every update, this calculator is run in a real browser with these known answers, and it must match all of them:

Jan 31, 2024 + 1 month = Feb 29, 2024 (month-end rule) ✓
Oct 27, 2026 + 90 days = Jan 25, 2027 ✓
Oct 27, 2026 − 2 weeks = Oct 13, 2026 ✓
Nov 20, 2026 + 5 business days, skipping Thanksgiving = Nov 30, 2026 ✓

Last checked October 26, 2026. Spotted something wrong? The math is done in your browser with the formula shown on this page, so you can check any result by hand.

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<p style="font:14px/1.4 sans-serif;margin:4px 0 0"><a href="https://calcist.com/date-calculator/">Date calculator</a> by Calcist</p>
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Questions people ask

What date is 90 days from today?

Leave the start date empty, choose Add and enter 90 days. From October 27, 2026, it's January 25, 2027.

What is January 31 plus one month?

February 28, or February 29 in a leap year. When the target month is shorter, the date moves to its last day.

How do I add business days to a date?

Choose Business days, enter the number and pick whether to skip US federal holidays. Weekends are always skipped, and the start date isn't counted.

How many weeks is 6 months?

It depends on the months, because they have different lengths. Six months is usually 181 to 184 days, or about 26 weeks.

Can I subtract to find a past date?

Yes. Choose Subtract. For example, October 27, 2026 minus 2 weeks is October 13, 2026.

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