Deadlines, notice periods, warranty windows and follow-up dates are all phrased as “so many days after” some starting point. This date calculator moves forward or backward from any date by years, months, weeks and days, or by business days that skip weekends and US federal holidays, and it shows exactly how it got there.
How to use the date calculator
- Pick the start date. It defaults to today.
- Choose Add to move forward in time or Subtract to move back.
- Choose Calendar time to enter years, months, weeks and days, or Business days to count working days only.
- Fill in the amounts. Leave any unit you do not need at 0.
- In business-day mode, keep Also skip US federal holidays ticked to step over observed holidays as well as weekends.
The tape shows the resulting date with its day of the week, how many calendar days apart the two dates are, and the ISO week number of the result.
How dates are added
Days and weeks are simple: every day is one step on the calendar and a week is seven of them. Months and years are different, because months run 28 to 31 days long. The calculator therefore works in two stages:
Adding months keeps the day of the month whenever that day exists. If it does not (the 31st in a 30-day month, or February 29 in a common year), the date is clamped to the last day of the target month. All arithmetic uses whole calendar days in UTC, so daylight saving time changes never shift the answer by an hour.
Business days
In business-day mode the calculator walks one day at a time from the start date, skipping Saturdays and Sundays and, if selected, observed federal holidays, until it has counted the number you asked for. Federal holidays are generated from the rules in federal law rather than a fixed list, so any year from 1971 onward works.
Worked examples
90 days after March 15, 2026. Ninety days is 12 weeks and 6 days. Counting forward lands on Saturday, June 13, 2026.
One month after January 31, 2025. There is no February 31, so the result is clamped to Friday, February 28, 2025. One year after February 29, 2024 is likewise February 28, 2025.
10 business days after Friday, October 9, 2026. The count skips two weekends plus Columbus Day on Monday, October 12, so the tenth business day is Monday, October 26, 2026, 17 calendar days later.
Common intervals from January 1, 2026
| Add | Result | Day of week |
|---|---|---|
| 30 days | January 31, 2026 | Saturday |
| 60 days | March 2, 2026 | Monday |
| 90 days | April 1, 2026 | Wednesday |
| 180 days | June 30, 2026 | Tuesday |
| 365 days | January 1, 2027 | Friday |
Notice that 365 days after January 1, 2026 is January 1, 2027 only because 2026 is a common year. Across a February 29 the same count stops one calendar day short of the anniversary, which is why contracts usually say “one year” rather than “365 days”.
Calendar days vs. business days
Legal and financial deadlines are written in both styles, and mixing them up is a common source of missed dates:
- Calendar days count every day, including weekends and holidays. Many notice periods, return windows and loan grace periods use them.
- Business days count Monday through Friday and usually exclude holidays. Federal agencies, courts and shipping carriers often use them, and many rules add that a deadline falling on a weekend or holiday moves to the next business day.
When you need to know how many days separate two dates you already have, use the date difference calculator; to count working days between them, use the business days calculator.
State holidays, bank-only closures and company shutdown days vary, so check your own calendar for anything beyond the federal list.
Frequently asked questions
What is 90 days from today?
Set the start date to today, choose Add, and enter 90 in the Days box. Because 90 days is 12 weeks and 6 days, the answer always falls one weekday earlier than today: 90 days after a Monday is a Sunday.
What happens when I add a month to January 31?
February has no 31st, so the date is moved back to the last day of February: February 28, or February 29 in a leap year. This month-end clamping is the same rule used by spreadsheets and most banking systems.
Is the start date counted?
No. Adding 1 day to Monday gives Tuesday. In business-day mode, counting also starts with the next working day, so 1 business day after a Friday is the following Monday.
Which holidays are skipped in business-day mode?
The eleven US federal holidays on their observed dates: when a holiday falls on a Saturday it is observed on Friday, and when it falls on a Sunday it is observed on Monday. State, bank-only and company holidays are not included.
In what order are years, months, weeks and days applied?
Years and months are applied first as calendar months, then weeks and days are added as a block of days. So January 30, 2025 plus 1 month and 1 day is February 28 plus 1 day, or March 1. Adding the day first would give January 31 plus 1 month, which is February 28.