"What date is 90 days from today?" "What was the date 6 months ago?" "When does my 30-day trial end?" These are simple questions that trip people up every time because months have different lengths and weekends aren't evenly spaced.
The Add / Subtract Date Calculator gives you the exact answer in seconds — add or subtract any number of days, weeks, months, or years from any starting date.
How to Add or Subtract from a Date
- Open the Add / Subtract Calculator
- Select your start date
- Choose Add or Subtract
- Enter the amount and select the unit (days, weeks, months, or years)
- See the result date instantly
No manual counting, no calendar flipping, no off-by-one errors from month-length differences.
Why Date Math Is Tricky by Hand
Months Have Different Lengths
Adding "1 month" to January 31 is ambiguous by hand. February has no 31st. The correct answer is February 28 (or 29 in a leap year) — not March 2 or March 3. Our calculator uses end-of-month semantics: adding a month moves to the same day of the next month, clamped to the last day if the target month is shorter.
Leap Years Change February
Adding 1 year to February 29, 2024 lands on February 28, 2025 — not February 29 (which doesn't exist in 2025). The calculator handles this correctly.
Weeks vs. Days
7 days and 1 week are equivalent, but "3 weeks" and "21 days" can give different intuitions when you're mentally anchoring to weekdays. The calculator lets you choose the unit that matches your context.
Common Use Cases
What Date Is 30 / 60 / 90 Days From Today?
The most searched date question on the internet. This comes up constantly in:
- Payment terms — Net 30, Net 60, Net 90 invoice due dates
- Free trial expirations — "Your 30-day trial ends on..."
- Probationary periods — First 90 days of employment
- Legal deadlines — Response windows expressed in calendar days
Calculate 30 days from today →
Contract Deadline Calculation
Contract signed: March 15, 2025
Response window: 30 calendar days
→ Add 30 days to March 15 → April 14, 2025
Note: April has 30 days, so adding 30 to March 15 doesn't land on April 15 — it's April 14. Manual counting often gets this wrong.
Subscription and Trial Expiry
Trial started: October 8
Trial length: 14 days
→ Add 14 days to October 8 → October 22
If the trial started on October 28, adding 14 days → November 11 (crosses the month boundary correctly).
Calculating a Due Date or Deadline
Deadline types by unit:
- "File within 30 days" → Add 30 days
- "Due in 6 weeks" → Add 6 weeks
- "Renew within 3 months" → Add 3 months
- "Valid for 2 years" → Add 2 years
Each unit behaves differently and choosing the right one matters. Adding "1 month" to January 31 ≠ adding "31 days" to January 31. The first gives February 28/29; the second gives March 2/3.
Working Backwards: What Date Was N Days Ago?
Use the Subtract direction to go backwards:
- "90 days ago" from today
- "6 months before" a deadline
- "2 years prior" to a contract date
Useful for:
- Statute of limitations calculations ("event occurred more than 3 years ago?")
- Warranty start dates ("purchased 18 months ago, what date was that?")
- Historical research
Warranty and Guarantee Periods
Product purchased: July 4, 2024
Warranty: 1 year
→ Add 1 year to July 4, 2024 → July 4, 2025
For extended warranties:
- 2-year warranty → Add 2 years
- 18-month warranty → Add 18 months (or 548 days — the month-based addition is more accurate for warranty terms)
Age and Milestone Planning
How old will you be on a specific date? Combine tools:
- Use Age Calculator mode with the "as of" date set to the future date
- Or add years to your birthday using Add / Subtract
What date will you turn 65? Add 65 years to your birthdate. What date will your child turn 18? Same approach.
Visa and Travel Date Calculations
Many visa rules use calendar days:
- "Must enter within 90 days of issue" → Add 90 days to the issue date
- "Maximum stay: 180 days in any 365-day period" → Add and subtract to map your travel windows
- "Passport must be valid for 6 months beyond departure" → Add 6 months to your departure date to find the minimum passport expiry
Medication and Health Schedules
- "Take for 14 days" — add 14 days to the start date for the end date
- "Follow-up appointment in 6 weeks" — add 6 weeks to today
- "Vaccine booster after 6 months" — add 6 months to the first dose date
Units Explained
Days
The most literal unit. 1 day = exactly 24 hours (ignoring DST transitions). Best for:
- Payment terms (Net 30)
- Legal deadlines
- Shipping and delivery estimates
- Short-term project windows
Weeks
1 week = 7 days exactly. Useful when you naturally think in weeks — sprint lengths, school terms, recovery periods.
Months
1 month = same day next month, clamped to the last day if shorter. A 3-month period from January 31 ends April 30 (not May 1 or May 2). Use months for:
- Subscription billing cycles
- Rental and lease terms
- Quarterly deadlines ("3 months from now")
- Medical and pregnancy milestones
Years
1 year = same day next year, handling February 29 → February 28 in non-leap years. Use for:
- Annual renewals
- Birthday calculations
- Multi-year contracts
- Tax year calculations
Examples by Scenario
Invoice Due Dates
| Invoice date | Terms | Due date |
|---|---|---|
| March 1 | Net 30 | March 31 |
| March 1 | Net 60 | April 30 |
| March 31 | Net 30 | April 30 |
| October 31 | Net 30 | November 30 |
| January 31 | 1 month | February 28 (or 29) |
Common "Days From Now" Lookups
(Dates are examples — use the calculator for today's actual result)
| Days | Approx. weeks | Common uses |
|---|---|---|
| 7 | 1 week | Short deadlines |
| 14 | 2 weeks | Notice periods, short trials |
| 30 | ~4.3 weeks | Net 30, trials, probation start |
| 45 | ~6.4 weeks | Extended payment terms |
| 60 | ~8.6 weeks | Net 60 invoices |
| 90 | ~12.9 weeks | Probationary period, Net 90 |
| 180 | ~25.7 weeks | 6-month review, visa rules |
| 365 | 52.1 weeks | Annual renewal, warranty |
Frequently Asked Questions
What is 30 days from today?
Use the Add / Subtract Calculator with today's date and "Add 30 days." The exact answer depends on today's date — the calculator updates it in real time.
What's the difference between "add 1 month" and "add 30 days"?
They're different. "1 month" means same day next month: January 15 + 1 month = February 15. "30 days" means exactly 30 × 24 hours: January 15 + 30 days = February 14. For subscription and contract terms, the month-based calculation is almost always what's intended. For legal calendar-day counting, use days.
What if the result date doesn't exist?
If adding a month would land on a day that doesn't exist (e.g., January 31 + 1 month = February 31), the calculator clamps to the last valid day of the month (February 28 or 29). This is the standard behavior used in most financial and legal contexts.
Can I add business days instead of calendar days?
The Add / Subtract mode works in calendar days, weeks, months, or years. For business day calculations, use the Business Days tab to count working days between two dates, or manually add days while counting forward to skip weekends.
How do I calculate what date is X days from a specific date (not today)?
Select your specific date as the start date in the calculator — it doesn't have to be today. Enter your amount, choose your unit, and the result will be relative to your chosen start date.
Related Tools
- Add / Subtract Dates — Find a date N days/weeks/months/years away
- Business Days Calculator — Count working days with holiday exclusion
- Date Difference Calculator — Days between any two specific dates
- Countdown Calculator — Live timer to a future date
Keep Reading
- How to Calculate Days Between Dates — The complete guide to date math
- Business Days Calculator Guide — Working days with country holiday exclusion
- Days Until Your Next Event — Live countdown to any date