Add Days to Date Calculator — add or subtract days, weeks, months, years

Real-world use cases

• Calculate a contract expiry date

  A service agreement is signed on 2026-01-31 with a term of "12 months from signing". You set the start date, switch to add, enter 12 in the months field, and read back 2027-01-31. When a contract starts on a month-end day the month-end clamp matters — a 1-month renewal from January 31 correctly lands on February 28, not an invalid date, so the expiry you record matches what a court would read the clause to mean.

• Find a loan or invoice due date

  An invoice dated today is due "net 45 days". Enter the issue date, add 45 in the days field, and you get the exact due date plus its weekday — handy because a due date that falls on a Saturday usually means you want to chase payment the Friday before. For a payment that must land on a working day, flip on business-day mode and count 45 business days instead.

• Estimate a pregnancy due date

  The common rule of thumb is 280 days (40 weeks) from the last menstrual period. Enter that date, add 40 in the weeks field, and the tool returns the estimated due date and which weekday it falls on. Because every month length and leap day is handled exactly, the estimate does not drift the way a flat "9 months" shortcut does.

• Track a visa or permit day count

  A visa allows a 90-day stay from the entry date. Enter your arrival date, add 90 days, and you get the last lawful day plus the "days from today" line so you can see how much time is left at a glance. Subtract mode answers the reverse: if you must leave by a fixed date, count back to find the latest day you could have entered.

• Set a project milestone from a kickoff

  A project kicks off on a Monday and the plan allots "15 working days" to the first phase. Turn on business-day mode, add 15 days, and the tool skips the weekends to give the real deadline — three calendar weeks out, not just 15 calendar days. Share the resulting URL with the team so everyone sees the same computed date.

Common pitfalls

• Using the Months field when you mean a fixed number of days. "30 days" and "1 month" are different — one month from January 31 is February 28, which is 28 days, not 30. Pick the field that matches the contract wording.

• Forgetting that business-day mode ignores the Years, Months, and Weeks fields. In that mode only the Days field is read, and it counts working days; the other fields are greyed out on purpose.

• Assuming business days already exclude public holidays. They do not — only Saturdays and Sundays are skipped. Holidays vary by country and year, so subtract any that fall in your span yourself.

Privacy