Date Calculator

How the date calculator counts

1. Pick the start date. It starts on today’s date on your device.
2. Choose Add or Subtract, and Calendar days or Business days.
3. Enter the period. In calendar mode you can mix years, months, weeks and days — the calculator adds the years and months first, then the weeks and days.
4. Read the answer: the weekday and date, the same date as 1/5/2027 and 2027-01-05 for forms and spreadsheets, how many calendar days away it is, and every step under How it’s calculated.

The start date itself is never counted: 1 day after Monday is Tuesday. The table under the calculator shows the common deadlines from your start date at a glance; Share copies a link that opens the same calculation.

Adding months: what happens at the end of a month

Months have 28 to 31 days, so adding a month keeps the same day number — and when that day does not exist, uses the last day of the month:

When this happens the calculator says so under the answer. timeanddate, calculator.net and Excel’s EDATE give the same dates. February has 29 days in leap years — every year divisible by 4, except century years not divisible by 400 (U.S. Naval Observatory).

Business days and federal holidays

In Business days mode the calculator walks forward (or back) one day at a time from the day after your start date, counting only Monday to Friday. With Skip federal holidays on, it also skips the 11 U.S. federal holidays on the day they are observed: a Saturday holiday on the Friday before and a Sunday holiday on the Monday after (5 U.S.C. 6103, OPM). The answer is always a business day, and the holidays it skipped are listed.

Some calculators count the start date as the first business day and can land on a Saturday; others use the holidays of the country your internet connection appears to be in. State holidays and company days off are not included here — switch the holiday option off if your workplace stays open on federal holidays. For the business days between two dates, use the days between dates calculator.

Common deadlines

When a deadline falls on a weekend, many businesses and offices move it to the next business day — check the terms that apply. If you need a share of a period, the percentage calculator does the division: 30 days out of a 90-day window is 33.3%. For a bill that covers part of a month — 25 days of a 30-day month is 25/30 — the fraction calculator reduces it to 5/6.

Adding days in Excel and Google Sheets

Format the result cell as a date. WORKDAY needs the holiday dates in a range (H1:H11 here): use the observed days from OPM’s list. Google Sheets has the same functions.

Counting legal and contract deadlines

Court rules and contracts often have their own counting rules: courts in the U.S. usually leave out the day of the event, count every calendar day after it, and move a deadline that lands on a weekend or holiday to the next business day. Rules differ by court, state and contract, so read the one that applies — this calculator adds calendar days and business days; it does not give legal advice.

For hours and minutes between two dates and times, a time duration calculator is on the way.