Add or subtract days, weeks, months and years to any date and read the result with its weekday, ISO week and day of year. You can also find out what the date was N days ago.
What was the date N days ago?
How the date calculator works
Enter a start date, choose whether to add or subtract, and fill in any mix of years, months, weeks and days. The calculator applies years and months first and weeks and days afterwards, then shows the result with its weekday, ISO week number and day of the year. "Today" always means the date in Brasília according to the site clock, so the starting point is right no matter where you are.
The end-of-month rule
Months have different lengths, so adding months can land on a day that does not exist. The calculator then clamps to the last day of the target month. Examples: January 31 + 1 month = February 28 (February 29 in a leap year); March 31 − 1 month = February 28 or 29; August 31 + 1 month = September 30. Adding 12 months to February 29, 2028 gives February 28, 2029. This is the same convention used by spreadsheets and most programming languages.
Adding days is not the same as adding months
"90 days" and "3 months" are different amounts. From January 31, 2027, 90 days ends on May 1, while 3 months ends on April 30 (the clamped month end). For contracts, check whether the text says days or months, because it decides the deadline.
Common uses
- Deadlines and notice periods: +30, +60 or +90 days from the date a document is signed.
- Warranties and subscriptions: +1 year or +6 months from the purchase date.
- Pregnancy and baby milestones: add 280 days to the first day of the last period for an estimated due date.
- Looking back: use "What was the date N days ago?" to find the day of an event, an invoice or a symptom, with its weekday.
ISO week and day of the year
The ISO week starts on Monday, and week 1 is the one containing the first Thursday of the year. This is why December 29 can be week 1 of the next year and January 1 can be week 52 or 53 of the previous one. The day of the year counts from 1 on January 1 up to 365 (366 in leap years). Both are common in planning, payroll and logistics; a dedicated page lists the week number of the year.
To count the interval between two dates instead, use days between dates; for a live countdown to an event, see the countdown.