Add / Subtract Date Calculator
Add or subtract any number of days, weeks, months, or years from a start date to find the resulting date and day of the week — useful for deadlines, due dates, and planning.
Start Date & Offset
Resulting Date
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Working out today’s date…
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How It Works
This calculator shifts a start date forward or backward by an amount of days, weeks, months or years. Days and weeks are plain calendar-day counting that crosses month and year boundaries correctly, leap years included. Months and years keep the same day of the month where it exists: 15 March + 2 months is 15 May. When the target month is shorter, the result is the last day of that month: 31 January + 1 month is 28 February (29 February in a leap year), and 31 March − 1 month is 28 February. The result also shows the day of the week, which helps when you need to know whether a deadline, anniversary or due date falls on a weekday or a weekend.
Formula
Days/weeks: calendar-day counting. Months/years: same day of the month, or the last day of the target month if it is shorter (31 Jan + 1 month = 28 Feb; 29 Feb 2028 + 1 year = 28 Feb 2029).
Adding Days to a Date
Counting forward from Thursday, 1 January 2026, these are the jumps people ask about most. Put your own start date in the calculator above to get yours.
| Days added | Resulting date |
|---|---|
| 7 | Thursday, 8 January 2026 |
| 14 | Thursday, 15 January 2026 |
| 30 | Saturday, 31 January 2026 |
| 45 | Sunday, 15 February 2026 |
| 60 | Monday, 2 March 2026 |
| 90 | Wednesday, 1 April 2026 |
| 100 | Saturday, 11 April 2026 |
| 120 | Friday, 1 May 2026 |
| 180 | Tuesday, 30 June 2026 |
| 365 | Friday, 1 January 2027 |
Adding Weeks to a Date
A week is always 7 days, so weeks convert to days with no surprises. The same start date, Thursday, 1 January 2026:
| Weeks added | Days | Resulting date |
|---|---|---|
| 1 | 7 | Thursday, 8 January 2026 |
| 2 | 14 | Thursday, 15 January 2026 |
| 4 | 28 | Thursday, 29 January 2026 |
| 6 | 42 | Thursday, 12 February 2026 |
| 8 | 56 | Thursday, 26 February 2026 |
| 10 | 70 | Thursday, 12 March 2026 |
| 12 | 84 | Thursday, 26 March 2026 |
| 26 | 182 | Thursday, 2 July 2026 |
| 40 | 280 | Thursday, 8 October 2026 |
| 50 | 350 | Thursday, 17 December 2026 |
| 52 | 364 | Thursday, 31 December 2026 |
40 weeks is 280 days, the length used for pregnancy due dates; the pregnancy due date calculator does that calculation from the last period date.
Adding Months and Years: What Happens at Month-End
Months have different lengths, so "one month later" needs a rule for dates like the 31st. This calculator keeps the same day of the month when it exists. When it does not, the result is the last day of the month you land in.
| Start date | Change | Result |
|---|---|---|
| 31 January 2026 | + 1 month | 28 February 2026 |
| 31 January 2028 | + 1 month (leap year) | 29 February 2028 |
| 31 March 2026 | − 1 month | 28 February 2026 |
| 30 April 2026 | + 1 month | 30 May 2026 |
| 31 May 2026 | + 3 months | 31 August 2026 |
| 29 February 2028 | + 1 year | 28 February 2029 |
The same rule applies when you subtract, which is why 31 March minus one month is 28 February 2026 and not a date in March. It also means month steps are not always reversible: 28 February plus one month is 28 March, not 31 March.
Days, Weeks, Months and Years Are Not Interchangeable
Pick the unit that matches how your deadline is written. A "30-day" notice and a "1-month" notice can end on different dates, and 52 weeks is a day short of a year.
| Compare | Result | With | Result |
|---|---|---|---|
| 30 days | 31 January 2026 | 1 month | 1 February 2026 |
| 52 weeks | 31 December 2026 | 1 year | 1 January 2027 |
| 365 days | 31 December 2028 (from 1 January 2028) | 1 year | 1 January 2029 |
Start date is 1 January 2026 unless stated.
Calendar Days or Working Days?
This calculator counts every calendar day, weekends and holidays included. If a deadline is written in business days, use the working days calculator, and to count the gap between two dates use the date difference calculator.
Frequently Asked Questions
How do I find the date 90 days from today?
Set the start date to today, choose "Add", enter 90, and select "Days". The calculator instantly shows the resulting date and its day of the week.
What happens when adding a month to the 31st of a month?
The result is the last day of the target month. Adding 1 month to 31 January gives 28 February (29 February in a leap year), and adding 1 month to 31 March gives 30 April. Subtracting works the same way: 31 March minus 1 month is 28 February.
Can I subtract time to find a past date?
Yes — switch to "Subtract" and enter the amount and unit (days, weeks, months, or years) to find a date in the past, e.g., "90 days before 15 March 2026."
Does this account for leap years?
Yes — day and week arithmetic automatically accounts for real calendar lengths, including the extra day in leap years (February 29).
What is this useful for?
Common uses include finding contract/warranty expiry dates, loan or subscription renewal dates, project deadlines a fixed number of days out, and confirming what day of the week a future or past date fell on.