➕ Date Calculator: Add or Subtract
What date is 90 days from today? 6 months after a contract date? 10 business days before a deadline? Get the exact date and weekday.
Common periods at a glance
How to use the date calculator
Choose a start date, add or subtract, then enter an amount and a unit. The resulting date and its day of the week appear instantly. Typical questions: "what date is 90 days from today?", "when is 6 months after my lease starts?", "what's 30 business days before the closing date?". The table underneath shows the most common periods (7, 30, 60, 90 and 100 days, 1/3/6 months, 1–2 years, 10 and 30 business days) from the same start date.
Rules for each unit
- Days Calendar days.
01/01/2026 + 100 days = 04/11/2026 - Weeks
N × 7 days— the weekday stays the same. - Months Moves to the same day of the month; if that day doesn't exist, the last day of the month is used.
Jan 31 + 1 month = Feb 28(Feb 29 in leap years),Mar 31 − 1 month = Feb 28. - Years The same as 12 months.
Feb 29, 2024 + 1 year = Feb 28, 2025 - Business days Skips Saturdays and Sundays. Friday + 1 business day is the following Monday. Public holidays are not skipped.
Adding months isn't reversible
Because of the month-end rule, Jan 31 + 1 month − 1 month = Jan 28. If you split a period into pieces you may get a different answer, so always calculate from the original date in one step. Banks and card issuers typically use the same month-end rule for maturity and due dates.
"N days after" vs. "the Nth day"
"100 days from today" is today + 100 days. But when today counts as day 1 — a 100-day challenge, a baby's 100th day, a Korean couple's 100-day anniversary — the 100th day is today + 99 days. Pick the Counting days option that fits; it has no effect on weeks, months or years.
Common uses
| Question | Enter |
|---|---|
| Return window / 30-day trial ends | Purchase date + 30 days |
| 90-day probation or visa-free stay | Start or entry date + 90 days (check whether the entry day counts) |
| Lease or contract renewal | Start date + 6 or 12 months |
| Invoice due (net 30) | Invoice date + 30 days |
| Shipping or processing time | Order date + N business days |
Legal deadlines
Many legal systems — including the US Federal Rules of Civil Procedure (Rule 6) and Korea's Civil Act — exclude the day of the triggering event and, if the last day lands on a weekend or legal holiday, extend the deadline to the next business day. This calculator's default ("start counting the next day") matches the first rule, but it does not automatically move weekend or holiday results, so check the next business day yourself.
Business-day results ignore public holidays (federal, state or national). For court, tax, immigration or contract deadlines, rely on the official rules and the relevant authority.