Date Add/Subtract
Add or subtract days, weeks, months, or years from a date
About the Calculator
Date math is deceptively hard. Add 30 days to January 15 and you land in February - but add 30 days to January 31 and you have to decide what happens when the result overshoots the end of February. Add 6 months to August 31 and February 28 or 29 is the only available answer. This calculator handles all of that automatically: pick a start date, choose whether to add or subtract, and select your unit - days, weeks, months, or years. Use it for invoice due dates, warranty expiry, contract terms, project deadlines, or any planning question that starts with "what date is X from now?"
How to Calculate Manually
- 1Select your starting date.
- 2Choose whether to add or subtract time.
- 3Enter the amount of time.
- 4Select the unit (days, weeks, months, or years).
- 5The result shows the calculated date.
Result Date
Saturday, June 27, 2026
Examples
What date is 90 days from January 1, 2026?
January has 31 days, so 30 remaining from Jan 1. February 2026 has 28 days (not a leap year). That's 58 days total. We need 32 more days into March = April 1. Result: April 1, 2026 - and note this is also exactly the Q1 end date, making it a natural quarterly deadline marker.
What was the date 6 months before July 15, 2026?
6 months back from July is January, same day. Result: January 15, 2026. Month subtraction keeps the day number unless end-of-month clamping is needed.
What date is 30 business days from May 8, 2026?
30 calendar days would give June 7. But 30 business days - skipping weekends - lands on June 19, 2026 (approximately, depending on public holidays). For business-day calculations, use the Business Days From Today calculator rather than this one.
When does a 2-year warranty purchased on March 1, 2025 expire?
Add 2 years to March 1, 2025 = March 1, 2027. Always add years rather than 730 days - a leap year in the range would make the day-count method land on February 29 or March 2.
FAQ
What's the difference between adding days vs. adding months?
Adding days is always exact - 30 days from any date is precisely 30 x 24 hours forward. Adding months keeps the same calendar day where possible, but clamps to the last day of the month when needed (e.g. Jan 31 + 1 month = Feb 28). For contracts and invoices, check which unit your terms specify.
What does "Net 30" mean exactly?
Net 30 is a payment term meaning the invoice is due 30 calendar days after the invoice date. Enter your invoice date, add 30 days, and that's your deadline. Net 60 and Net 90 work the same way.
Can I calculate business days instead of calendar days?
This calculator uses calendar days only. For business day calculations - excluding weekends and public holidays - use the Business Days From Today or Business Days Before Today calculators.
What happens when adding months overshoots the end of the month?
The result clamps to the last valid day of that month. Adding 1 month to January 31 gives February 28 in regular years, February 29 in leap years. This matches how most banks, legal contracts, and invoicing systems handle it - but always verify for specific contractual contexts.
Can I add years to a date?
Yes - select "Years" from the unit dropdown. Adding 1 year keeps the same month and day, except for February 29 birthdays in leap years, which clamp to February 28 in non-leap years.
Tips & Strategies
"Net 30" means 30 calendar days, not business days. Enter your invoice date, add 30 days, and that's your payment due date. If your terms are Net 60 or Net 90, same logic - just change the amount. For business-day terms, use the Business Days From Today calculator instead.
Adding months respects end-of-month boundaries. One month after January 31 is February 28 (or 29 in leap years), not March 3. The calculator handles this automatically - but if your contract specifies a different convention, verify manually.
For warranty and subscription expiry, add 1 year to your purchase date. A product bought May 8, 2025 with a 1-year warranty expires May 8, 2026 - not 365 days later, which would be May 7 in non-leap years.
Subtract to find a start date from a known deadline. Working backwards from a June 30 deadline, subtract 90 days to find your project must have started April 1. This is useful for sprint planning, content calendars, and event timelines.
Cross-check when the decision matters. Run a second scenario with rounded inputs or a different path to the same quantity so you do not rely on a single fragile chain of arithmetic.
Things Worth Knowing
- •The Missing 11 Days: When Britain switched from the Julian to Gregorian calendar in September 1752, they skipped 11 days, going from September 2nd directly to September 14th, causing riots from people who thought their lives were "shortened."
- •Leap Year Complexity: Leap years occur every 4 years, except years divisible by 100 (skipped), except years divisible by 400 (kept), meaning 2000 was a leap year but 1900 wasn't and 2100 won't be.
- •The Unix Epoch Quirk: All computer systems count dates from January 1, 1970 00:00:00 UTC, meaning any date calculation before that requires "negative time," and dates before 1901 often break old systems.
- •Calendar Chaos: The world currently uses 40+ different calendar systems simultaneously; most use Gregorian for business, but countries also maintain Hebrew (5786), Islamic (1447 Hijri), Chinese (4723), and other calendars.
- •The 400-Year Pattern: The Gregorian calendar exactly repeats every 400 years (146,097 days), meaning the calendar for 2026 will be identical to 2426, and the last time it matched was 1626.
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