Date Calculator
Add or Subtract Time From Any Date
Calendar math sounds simple until you're counting across month-end boundaries, leap years, or trying to figure out what date falls exactly 90 days from today. This calculator handles all the edge cases so you get the right answer instantly — whether you're calculating a deadline, a due date, a warranty expiry, or a subscription renewal.
How to Use This Calculator
Enter a start date, choose whether to add or subtract time, and enter the number of years, months, and days to offset. You can combine all three — for example, add 1 year, 3 months, and 15 days in a single calculation. Hit Calculate Date to see the result date, the day of the week it falls on, and where it sits in the calendar year.
Common Real-World Uses
- Legal and contract deadlines — "90 days from signing" is one of the most common contractual time measurements. Enter your signing date and add 90 days.
- Warranty and subscription expiry — find exactly when a 1-year warranty expires or when a subscription auto-renews.
- Loan maturity dates — calculate when a 6-month or 18-month term loan comes due.
- Project planning — find a date that is 6 weeks or 3 months from your project start.
- Age milestones — calculate when someone turns a specific age on a future date.
- Medical follow-ups — "come back in 6 weeks" gives you the exact appointment window.
How Month-End Dates Are Handled
Adding months to dates near the end of the month requires special handling since months have different lengths. Adding 1 month to January 31 can't land on February 31 (which doesn't exist), so the result adjusts to the last valid day of the resulting month — February 28 (or 29 in a leap year).
This behavior matches how most banks, contracts, and software systems handle month-end date arithmetic. If the exact day matters for your use case (e.g., a loan payment date), verify with the relevant institution.
Leap Year Handling
The calculator automatically accounts for leap years. A year is a leap year if it is divisible by 4, except for century years which must be divisible by 400. This means 2000 was a leap year but 1900 was not. Over any 4-year period, this adds one extra day to calculations that span February 29.
What the Results Show
- Result Date — the exact date after adding or subtracting the specified time
- Day of Week — useful for scheduling (avoid weekends for deadlines, etc.)
- Day of Year — which numbered day of the year the result falls on (1–365/366)
- Days from Today — how far the result date is from the current date
- Week Number — ISO week number, useful for project scheduling
- Quarter — which business quarter the result date falls in
Frequently Asked Questions
What does "90 days" mean in a legal contract?
In most jurisdictions, "90 days" means 90 calendar days unless the contract specifies "business days." Calendar days include weekends and holidays. For a contract signed on June 1, 90 calendar days later is August 30. If the deadline falls on a weekend or holiday, check your contract — some specify the next business day, others the prior business day.
How is "6 months from today" different from "180 days"?
Significantly different. Six months from January 31 is July 31 — exactly 181 days (in a non-leap year). Six months from March 31 is September 30 — only 183 days. Calendar months don't have uniform length, so month-based calculations and day-based calculations produce different results. Use the appropriate unit for your context — contracts usually specify months, while legal deadlines often specify days.
Can I calculate a date in the past?
Yes — use the "Subtract" operation to go back in time. Enter any start date and subtract years, months, or days to find the earlier date. This is useful for finding anniversary dates, calculating when something happened relative to a known date, or working backwards from a deadline.
What's the difference between this and the Days Between Dates calculator?
This calculator starts with a date and adds or subtracts time to find a result date. The Days Between Dates calculator starts with two known dates and tells you how far apart they are. Use this one when you know the offset but not the end date; use Days Between Dates when you know both dates.
How do I find a date that is a specific number of business days away?
This calculator works in calendar days, not business days. For a rough estimate, multiply your business day count by 1.4 (since 5 business days = 7 calendar days) and add that many calendar days. For precision, count manually on a calendar skipping weekends — or use a dedicated business day calculator that accounts for local holidays.