About the Date Add & Subtract
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 the Date Add & Subtract
- Set the starting date, defaulting to today.
- Choose whether to add or subtract.
- Enter the offset in days, weeks, months, or years.
- 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.