Does the calculator include the start date?

No. The start date is day 0, so adding 1 day gives the next day. Subtract 1 if your rule counts the start day.

What happens when I add a month to 31 January?

The result is the last day of February — 28 February, or 29 February in a leap year.

Does business-day mode skip public holidays?

No, only Saturdays and Sundays. Public holidays differ by country, so adjust for them yourself.

What is the ISO week number?

The week of the year under ISO 8601: weeks start on Monday and week 1 is the one containing the first Thursday of the year.

Can I subtract years and months?

Yes. Choose subtract and enter any combination of years, months, weeks and days.

Time & Date · Free tool

Add or Subtract Days Calculator

Add or subtract days, weeks, months or years from a date — or count business days only.

"What date is 90 days from today?" is one of the most searched calendar questions — for notice periods, visa stays, warranty windows, payment terms and project deadlines. Counting on a calendar is slow and easy to get wrong across month ends and leap years. This calculator does it exactly.

Enter a start date, choose add or subtract, and set any mix of years, months, weeks and days. Years and months are applied first, then weeks and days. When a month step lands on a day that does not exist — 31 January plus one month — the result moves to the last day of the target month (28 or 29 February), the same convention most contracts and spreadsheet functions use, and the calculator tells you when that happened.

Switch on business-day mode to skip Saturdays and Sundays — useful for "10 working days" deadlines. Public holidays vary by country and are not removed, so check your local calendar for those.

By DailyCalc Editorial Team · Updated 2026-10-03 · 5-min read · 3 sources cited

● Date +/− calculator

Time & Date →

How the date is calculated

Result = clamp(start + years + months) + weeks × 7 + days; business mode: step one day at a time, counting only Mon–Fri

Adding months changes the month number and keeps the day, clamped to the month's length. Days and weeks are then added as exact 24-hour calendar days in the Gregorian calendar, so leap years (every 4 years, except century years not divisible by 400) are handled automatically. The ISO week shown follows ISO 8601: weeks start on Monday and week 1 contains the year's first Thursday.

start: The date you count from (not counted as day 1).
years, months, weeks, days: Whole numbers to add or subtract.
clamp: Moves an impossible day such as 31 February to the month's last valid day.

Worked examples: 90 days, 10 business days, and a month-end

Three common questions, starting from Saturday 3 October 2026:

3 Oct 2026 + 90 days: 28 days to the end of October, 30 in November, 31 in December = 89, so day 90 is 1 January 2027 — a Friday, ISO week 53 of 2026.
3 Oct 2026 + 10 business days: skip the weekend, count Mon 5 to Fri 9 (5) and Mon 12 to Fri 16 (10) → Friday 16 October 2026.
3 Oct 2026 − 30 days → Thursday 3 September 2026.
31 Jan 2026 + 1 month → 28 Feb 2026 (clamped). In leap year 2028 the same step gives 29 Feb 2028.
29 Feb 2024 + 1 year → 28 Feb 2025, because 2025 has no 29 February.

Result: 90 days after 3 Oct 2026 is Fri 1 Jan 2027; 10 business days after is Fri 16 Oct 2026.

How to use this date calculator

Set the start, the direction and the amount.

Step 1: Pick the start date

It defaults to today. The start date itself is day 0.

Step 2: Choose add or subtract

Subtract to find a date in the past, such as 30 days before a deadline.

Step 3: Enter years, months, weeks and days

Use any combination. Leave unused fields at 0.

Step 4: Business days (optional)

Tick the box to count Monday–Friday only. This mode counts days, so set years, months and weeks to 0.

Common uses

Deadlines that are defined as a number of days:

Notice periods

A 30- or 90-day notice period from the date you hand in notice.

Payment terms

Invoice due dates such as net 30 or net 60.

Travel and visas

Check the last day of a 90-day stay or a passport validity rule.

Returns and warranties

A 14-day return window or a 1-year warranty from the purchase date.

Working-day deadlines

"Reply within 10 working days" — use business-day mode, then remove any public holidays.

Pro tips

Avoid off-by-one surprises:

Check whether your deadline counts the start day. This calculator does not; if yours does, subtract one day.
For contracts, read how "month" is defined — a calendar month is not always 30 days.
Add public holidays back manually in business-day mode; they differ by country and region.
To count the days between two dates instead, use our date difference calculator.

Common mistakes

Where manual date counting fails:

Treating every month as 30 days

Adding 3 months is not the same as adding 90 days — from 3 October, 3 months is 3 January and 90 days is 1 January.

Forgetting leap years

Spans that cross 29 February in a leap year are one day longer.

Counting weekends as working days

10 working days is two calendar weeks, not 10 calendar days.

Ignoring month-end clamping

31 March plus one month is 30 April, not 1 May.

Sources & references

The formula, thresholds and guidance on this page were checked against these primary sources. Written and reviewed by DailyCalc Editorial Team; last updated 2026-10-03. Spotted an error? Tell us.

FAQs