Add Days to a Date Calculator

Enter a start date and an amount to get the date that many days, weeks, months or years later. A negative amount subtracts.

Runs in your browserFree, no sign-upLast reviewed October 8, 2026

Fill in the settings to see your result here.

Your result appears here instantly — nothing is uploaded.

Quick answers

How do I add days to a date?: Count forward that many calendar days from the start date, not counting the start date itself. Adding 30 days to May 20 gives June 19: 11 days take you to May 31 and the remaining 19 land on June 19. The calculator above does the same count for any date and amount.
How do I subtract days from a date?: Enter the amount as a negative number. With a start date of October 8, 2026 and an amount of -90 days, the result is Friday, July 10, 2026. The Days shifted figure shows -90 to confirm the direction.
What is 20 May plus 30 days?: June 19. May has 31 days, so 11 of the 30 days are used reaching May 31 and the other 19 fall in June. In 2026 that date is a Friday.
What is 90 days from October 8, 2026?: Wednesday, January 6, 2027. Ninety days is 12 weeks and 6 days, so the result always falls one weekday earlier than the start day: a Thursday start gives a Wednesday.
Is adding 1 month the same as adding 30 days?: No. One month moves to the same day number in the next month, which is 28 to 31 days away. October 8, 2026 plus 1 month is November 8 (31 days), while plus 30 days is November 7.
What is January 31 plus one month?: February 28, or February 29 in a leap year. There is no February 31, so the result stops at the last day of February instead of running over into March.

What Add or Subtract Days does

Pick a start date, type an amount and choose a unit, and the calculator returns the resulting date written out in full with its day of the week. To subtract, enter a negative amount such as -45. Days and weeks are exact calendar counts: 30 days after May 20 is June 19. Months and years keep the same day of the month where it exists and stop at the last day of the month where it does not, so January 31 plus one month is February 28, or February 29 in a leap year. Weekends and holidays are counted like any other day.

Date plus 30, 45, 60, 90, 100, 120, 180 and 365 days

A day count that is not a multiple of 7 moves the weekday forward by the remainder. The last column shows the real result for a start date of Thursday, October 8, 2026.

Days added	Weeks and days	Weekday moves forward by	From October 8, 2026
7	1 week	0 (same weekday)	Thursday, October 15, 2026
14	2 weeks	0 (same weekday)	Thursday, October 22, 2026
30	4 weeks 2 days	2	Saturday, November 7, 2026
45	6 weeks 3 days	3	Sunday, November 22, 2026
60	8 weeks 4 days	4	Monday, December 7, 2026
90	12 weeks 6 days	6	Wednesday, January 6, 2027
100	14 weeks 2 days	2	Saturday, January 16, 2027
120	17 weeks 1 day	1	Friday, February 5, 2027
180	25 weeks 5 days	5	Tuesday, April 6, 2027
365	52 weeks 1 day	1	Friday, October 8, 2027

Adding 365 days returns the same calendar date one year on only when no February 29 falls inside the span.

Worked examples in each unit

A 30-day window starting May 20

Start date May 20, 2026; Amount 30; Unit Days

Friday, June 19, 2026. ISO 2026-06-19, US 6/19/2026, European 19/06/2026, ISO week W25.

Counting back 90 days

Start date October 8, 2026; Amount -90; Unit Days

Friday, July 10, 2026. Days shifted -90, ISO week W28.

Six weeks ahead

Start date October 8, 2026; Amount 6; Unit Weeks

Thursday, November 19, 2026. Days shifted 42, ISO week W47.

Whole weeks always land on the same weekday as the start date.

A three-month review date

Start date October 8, 2026; Amount 3; Unit Months

Friday, January 8, 2027. Days shifted 92, ISO week W1.

Five years on

Start date October 8, 2026; Amount 5; Unit Years

Wednesday, October 8, 2031. Days shifted 1,826.

Adding months and years at the end of a month

When the target month is shorter than the start day, the result is the last day of that month. These rows are real outputs.

Start date	Shift	Result	Days shifted
January 31, 2026	+1 month	February 28, 2026	28
January 31, 2028	+1 month	February 29, 2028	29
January 30, 2026	+1 month	February 28, 2026	29
August 31, 2026	+1 month	September 30, 2026	30
December 31, 2026	+2 months	February 28, 2027	59
March 31, 2026	-1 month	February 28, 2026	-31
February 28, 2026	-1 month	January 28, 2026	-31
February 29, 2028	+1 year	February 28, 2029	365
February 29, 2028	+4 years	February 29, 2032	1,461

Month arithmetic does not always reverse: January 31 plus a month is February 28, but February 28 minus a month is January 28.

How the new date is calculated

Days: start + N days. Weeks: start + 7 x N days. Months: same day number N months later, capped at that month's last day. Years: the months rule with 12 x N months.

Days and weeks are counted on the calendar, so a leap day inside the span is simply one of the days. The start date is day zero, and the day after it is day 1. In a spreadsheet the same results come from =A1+30 for days, =A1+7*6 for weeks and =EDATE(A1,1) for months, which caps at the month end in the same way. The Amount is read as a whole number, so 2.5 is treated as 2, and it can be anything from -100,000 to 100,000.

Calendar days, not working days or 24-hour blocks

Every day counts here, including Saturdays, Sundays and public holidays. That is the right reading for terms written as plain days, such as a 30-day return window, 90-day payment terms or a 14-day notice. Check the Day of week in the result: a deadline that lands on a Saturday or Sunday is often moved to the next working day by the contract or rule that sets it.

If your deadline is written in business days or working days, a calendar count gives a date that is too early. Use the Add Business Days tool on this site for those; it skips weekends and the holidays you list.

The result is a whole date with no time of day attached. Clock changes for daylight saving time do not affect it, because the calculation moves between calendar dates and does not add up hours.

How to use it

1
Set the Start date. It opens on today's date.
2
Type the Amount (use a negative number to subtract), for example 90 to go forward or -90 to go back.
3
Choose the Unit: Days, Weeks, Months or Years.
4
Read the Resulting date, then use the Formats panel for the ISO (YYYY-MM-DD), US and European versions, the Day of week, Days shifted and ISO week.

Frequently asked questions

Does the start date count as day one?

No. The start date is day zero and the next day is day 1, so adding 1 day to a Monday gives Tuesday. If your rule counts the start date as the first day, enter one less than the number of days.

Can I add weeks, months or years as well as days?

Yes. Change Unit to Weeks, Months or Years. One unit is applied per calculation, so to add 1 year and 3 months, either enter 15 months or run the tool twice, using the first result as the second start date.

What does Days shifted tell me?

It is the number of calendar days between the start date and the result, negative when you subtracted. It is most useful after a months or years shift, where the day count is not obvious: 3 months from October 8, 2026 is 92 days, and 6 months is 182.

What is the difference between the US and European formats?

The US format puts the month first without leading zeros (1/6/2027) and the European format puts the day first with leading zeros (06/01/2027). The ISO format, 2027-01-06, is unambiguous and sorts correctly as text.

What is the ISO week shown in the result?

It is the ISO 8601 week number of the resulting date, where weeks start on Monday and week 1 is the week containing the first Thursday of the year. December 31, 2026 falls in W53, and January 6, 2027 falls in W1.

What happens when I add a year to February 29?

The result is February 28 of the following year, because that year has no February 29. Adding 4 years to February 29, 2028 gives February 29, 2032.

How do I find the number of days between two dates instead?

That is the opposite calculation. Use the Date Difference Calculator on this site: it takes two dates and returns the total days, weeks, months and years between them.