About Add to Date
Add to Date shifts a date forward by an amount you choose and reports the resulting calendar day. You supply a start date, a number and a unit — days, weeks, months or years — and it returns the new date in YYYY-MM-DD form.
Days and weeks are exact arithmetic: adding 14 days always moves forward two weeks regardless of how long the months in between happen to be. Months and years are calendar operations, which is normally what you want — adding one month to the 15th of January lands on the 15th of February, not on a fixed count of days.
That calendar behaviour has one well-known edge worth knowing. When the starting day does not exist in the target month, the date rolls over into the following month: the 31st of January plus one month cannot land on a 31st of February, so it spills into early March instead of clamping to the month end. If your dates cluster at month ends, read the result rather than assuming it stopped at the last valid day.
How to use Add to Date
- 1 Enter the starting date in YYYY-MM-DD format.
- 2 Type the amount to add; a negative number moves the date backward.
- 3 Choose whether the amount counts days, weeks, months or years, then read the resulting date.
Frequently asked questions
What happens when I add a month to the 31st?
It rolls over. There is no 31st of February, so the result spills into March. This is standard JavaScript calendar arithmetic rather than a defect, but it is easy to miss with month-end dates.
Can I subtract instead of adding?
Yes. Enter a negative amount to move the date backward. The unit still applies, so minus three months and plus three months are mirror operations.
Are weeks simply seven days?
Effectively yes. The weeks option multiplies the amount by seven and adds days, so it is unaffected by month lengths or by the calendar quirks that months and years carry.
Does the result account for daylight saving?
The output is a plain calendar date, so it is independent of clock changes. Even across a daylight-saving boundary the day count stays correct, because only the date is reported.
Free, online, and private
Free to use
Add to Date is completely free. There is no account to create, no login, and no hidden charge or usage limit.
Runs online in your browser
It is a free online tool that runs entirely in your browser. Nothing to download or install — open the page and start using it right away.
Your data stays private
All processing happens locally on your device. Your input is never uploaded, stored, or tracked, so it never leaves your browser.
How Add to Date behaves in detail
These are the specifics of this implementation — the exact ranges, defaults and fixed settings you are working with.
| Parameter | Value |
|---|---|
| Inputs | a date, an amount, and a unit — days, months, years or weeks (default 30 days) |
| Mechanism | setDate for days and weeks, setMonth for months, setFullYear for years |
| Output | an ISO date only — the first ten characters of the timestamp, so any time of day is discarded |
| Fallback branch | years is the else case, so any unit value other than days, weeks or months is treated as years |
| Default input | 2024-01-01 |
Compiled from the implementation of this tool and checked against it by itoolnet.
What Add to Date does not do
Knowing the edges of a tool saves more time than another list of its features. These are the cases where it will not do what you might expect.
- Month addition overflows instead of clamping. 2024-01-31 plus one month lands on 2024-03-02 rather than on the last day of February, because asking for 31 February is not possible and the surplus days roll forward into March without any notice.
- There is exactly one amount and one unit per run, so compound shifts such as six weeks and three days take two passes. No working-day or holiday logic is involved either — a Saturday is a perfectly acceptable answer here.
- Only the date part survives. Because the result is sliced from the ISO string, the time component disappears, the original input format is not echoed, and a typo that still happens to parse as a date goes through with no complaint at all.
Tested and documented by itoolnet, the team that builds and maintains this site.