Date Calculator
Pick a start date, add or subtract days, weeks, months, or years, and see the resulting date and weekday instantly.
Only applies when the unit is Days. Skips Saturdays and Sundays — public holidays aren't included.
Quick picks
Select a start date.
A date calculator for "what date is X from today" questions
Deadlines, contract terms, shipping windows, and reminders are almost always phrased in relative time — "in 30 days," "6 months from the signing date," "90 business days after delivery." Doing that arithmetic by hand means tracking how many days are left in the current month, whether a leap year is involved, and which weekday you land on. This calculator does it instantly: pick a start date (it defaults to today), choose how much to add or subtract and in what unit, and the resulting date appears with its weekday.
How the calculation works
Each unit is handled with real calendar math, not a fixed day-count approximation:
- Days — moves the calendar date forward or backward by exactly that many days.
- Weeks — multiplies by 7 and adds/subtracts that many days.
- Months — moves to the same day number in the target month, clamping to the last day of the month when the original day doesn't exist there (see the FAQ for the January 31 example).
- Years — same as months, using 12× the number of years, so February 29 on a leap-year start date clamps to February 28 in a non-leap target year.
Turning on Count business days only changes the Days unit to count Monday-through-Friday weekdays only, skipping every Saturday and Sunday as it steps toward the target count. It does not know about public holidays — see the FAQ below for why that's a deliberate scope limit, not an oversight.
Example 1 — a simple day count. Start date March 25, Amount 10, Unit Days, Direction Add. March has 31 days, so 6 days complete March (26–31) and the remaining 4 days land in April: the result is April 4.
Example 2 — month-end clamping. Start date January 31, Amount 1, Unit Months, Direction Add. February has no 31st day, so the calculator lands on the last valid day: February 28 in a common year, or February 29 in a leap year.
Example 3 — business days only. Start date a Friday, Amount 1, Unit Days, business-days-only turned on. Saturday and Sunday don't count as business days, so the 1 business day lands on the following Monday — not Saturday.
Days, weeks, months, or years — which unit should I pick?
| Use case | Suggested unit |
|---|---|
| "30/60/90 days from today" | Days |
| Shipping or return windows quoted in business days | Days + business-days-only |
| Sprint or billing cycles quoted in weeks | Weeks |
| Contract terms, notice periods, "6 months from signing" | Months |
| Warranty periods, anniversaries, age-related dates | Years |
Common mistakes to avoid
- Assuming "1 month" always means "30 days." It doesn't — months range from 28 to 31 days, so month-based and day-based arithmetic can land on different dates for the same nominal period.
- Forgetting that "business days" and "calendar days" diverge quickly. 10 business days is roughly 14 calendar days once two weekends are factored in, not 10.
- Chaining month additions instead of adding once. Adding 1 month twice in a row can land on a different date than adding 2 months directly, because each step clamps independently — see the FAQ for a worked example.
Sources & further reading
- NIST Time and Frequency Division — official U.S. civil timekeeping, leap seconds and calendar time standards
- ISO 8601 — the international standard for writing dates, durations and time intervals
- MDN Web Docs: JavaScript Date — how date arithmetic and month overflow behave in browsers
- U.S. OPM Federal Holidays — the official holiday list used for business-day counting
Frequently asked questions
What date is 30 days from today?
Set Start date to today (the default), Amount to 30, Unit to Days, and Direction to Add — the resulting date and weekday appear instantly above. The same method works for any number, such as 60, 90, or 180 days from today. As a worked example, 10 days from March 25 lands on April 4, since March has 31 days: 6 days finish out March and the remaining 4 days carry into April.
Why does adding 1 month to January 31 give February 28?
Because February never has 31 days, the calculator adjusts to the last valid day of the target month — February 28 in a common year, or February 29 in a leap year such as 2028. The adjustment is based on the original start date, not chained: adding 2 months to January 31 gives March 31 directly, which can differ from adding 1 month twice in a row (January 31 → February 28 → March 28). This is standard calendar-month arithmetic, not a bug.
Does 'business days only' account for public holidays?
No. With that option on, the calculator counts only Monday through Friday and skips every Saturday and Sunday — a pure weekday count. It doesn't know about public holidays in any specific country, since holiday calendars differ widely by region and change every year. The option is only available when the unit is set to Days.
Can I subtract days, weeks, months, or years instead of adding them?
Yes. Switch Direction to Subtract and the calculator counts backward from the start date instead of forward — useful for questions like 'what date was 90 days ago' or 'what date was 6 months before this deadline.' The business-days-only option also works in reverse, skipping weekends as it counts back.
Is my date data sent to a server?
No. This date calculator runs entirely in your browser — the start date, amount, and every calculation stay on your device and are never uploaded or stored on a server. Your last inputs are saved only in your browser's local storage, so the tool remembers them the next time you open it.