Add or Subtract Days from a Date

Deadlines are almost always expressed as an offset — 30 days from invoice, 90 days from filing, six weeks from today — and turning that into an actual calendar date is where mistakes creep in. Enter a start date and an offset, and this tool returns the exact date and which day of the week it falls on.

How to use it

1. Set the starting date, defaulting to today.
2. Choose whether to add or subtract.
3. Enter the offset in days, weeks, months, or years.
4. Read the resulting date, its weekday, and the ISO format for copying into software.

Frequently asked questions

What happens when adding a month lands on a date that does not exist?

Adding one month to 31 January would give 31 February, so the result is clamped to the last valid day of the target month — 28 or 29 February. This matches how most calendar software behaves.

Why does the weekday matter?

Because deadlines that fall on a weekend usually roll to the next working day in contracts and court filing rules. Seeing the weekday immediately tells you whether that applies.

Can I count business days instead?

This tool works in calendar days. For working-day counts between two known dates, use the date difference calculator with the weekdays-only option.

Which date format should I copy?

ISO 8601, shown alongside the result. YYYY-MM-DD is unambiguous worldwide, unlike 03/04/2026 which means two different days depending on the country.

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