Date Calculator - Add or Subtract Days, Weeks, Months or Years from a Date
Start from any date and add or subtract years, months, weeks and days to get the new date and its weekday.
Maintained by Hirantha Sandaruwan Lakshan. Updated 13 October 2026.
About this tool
Or switch to working days to find the date 10 or 30 working days away, skipping weekends and, if you want, Sri Lanka's public holidays. It runs in your browser and sends nothing anywhere.
How it works
In calendar mode the tool applies years and months first, where a year counts as twelve months. A day that does not exist in the month reached becomes that month's last day, so 31 January plus one month is 28 February (29 in a leap year) and 29 February plus one year is 28 February. Subtracting follows the same rule backwards.
Weeks and days are applied after the months, as plain calendar days, so the order matters. Adding 1 month and 1 day to 30 January 2026 gives Sunday 1 March 2026: the month first makes 28 February, then one more day. Adding the day first would give 31 January, and a month after that is 28 February.
Working-day mode steps forward (or back) one day at a time and counts only Monday to Friday. The start date is not counted, so one working day after a Friday is the next Monday, and a start date on a weekend begins with the next working day. Zero working days gives the start date. With the holiday option on, Sri Lanka public holidays on weekdays are skipped too, for 2026 and 2027 only. Outside those years only weekends are skipped, and the tool warns you.
The date is a calendar date, with no time of day and no time zone, so daylight saving cannot move the answer. 'Today' means today in Sri Lanka (Asia/Colombo, UTC+5:30). The tool covers the years 1583 to 9999.
Worked examples
90 days from 13 October 2026
Add 90 days and you get Monday 11 January 2027, day 11 of the year. Subtract the same 90 days from that date and you are back on 13 October 2026.
Month ends: 31 January plus one month
31 January 2026 plus 1 month is Saturday 28 February 2026. In the leap year 2028 the same sum gives Tuesday 29 February 2028. Subtracting works the same way: 31 March 2026 minus 1 month is Saturday 28 February 2026.
Five working days from Friday 10 April 2026
Skipping weekends only, the fifth working day is Friday 17 April 2026. Skipping Sri Lanka public holidays too (the New Year holidays on 13 and 14 April), it is Tuesday 21 April 2026.
Frequently asked questions
What is the date 90 days from today?
Leave the start date as today, choose Add, and enter 90 in the Days box. For example, 90 days after 13 October 2026 is Monday 11 January 2027.
What is 31 January plus one month?
28 February 2026 in 2026, and 29 February 2028 in the leap year 2028. February has no 31st, so the tool uses its last day. Some programs roll the extra days over into March instead, so another tool may give a different answer.
How do I add working days to a date?
Choose 'Working days (Mon to Fri)', enter the number and pick whether to skip Sri Lanka public holidays as well. The start date is not counted, and Saturdays and Sundays are always skipped.
Is a month 30 days?
No. The tool adds calendar months. Adding 1 month to 15 January 2026 gives 15 February, 31 days later, but adding it to 15 February gives 15 March, 28 days later.
Does adding days count the start date?
No. One day after 1 January is 2 January. In working-day mode the start date is not counted either.
What happens if I add one year to 29 February?
You get Friday 28 February 2025 for 29 February 2024, the last day of February in the next year. Add four years and you reach Tuesday 29 February 2028.
Are Sri Lanka public holidays included?
Only when you choose them, in working-day mode, and only for 2026 and 2027, taken from the Central Bank of Sri Lanka's lists of public and bank holidays. The lists mark only some of them as mercantile holidays, so a private employer's days off can differ. Outside those years the tool skips weekends only and says so.
Sources & references
Updated Oct 13, 2026