Date Calculator
Add or subtract years, months, and days from a specific date.
Whether you are tracking project deadlines, planning a wedding, or counting down to a vacation, dates are central to our lives. But adding "90 days" to "March 15th" in your head is frustrating and prone to error. Our Date Calculator handles the calendar math for you, accounting for the variable lengths of months and even leap years, to give you an exact future or past date instantly.
Date Operation
Resulting Date
Frequently Asked Questions
Why Date Math is Complex
Calculating dates manually is deceptively difficult. It's not just base-10 math; it's a mix of base-12 (months), base-7 (weeks), and base-28/29/30/31 (days). One small mistake can throw off a project schedule by days.
1. The Leap Year Rule
We add a leap day (Feb 29) every 4 years. The rule is strictly algorithmic:
- Divisible by 4? Yes (Leap year).
- ...Unless divisible by 100? No (Skip it).
- ...Unless divisible by 400? Yes (Put it back).
This is why the year 2000 was a leap year, but 1900 was not. Our calculator handles this logic invisibly in the background.
2. Time Zones & Epochs
Computers store dates as the number of milliseconds since January 1, 1970 (UTC), known as the Unix Epoch. This creates a standardized way to track time globally, regardless of your local time zone. When you see a computer date bug showing "Dec 31, 1969", it usually means the timestamp value is 0 or -1, defaulting to the epoch start.
3. Frequently Asked Questions (FAQ)
Q: Does this include business days?
No, this calculator adds calendar days (including weekends and holidays). For project management, you typically need to exclude non-working days.
Q: What about Julian Calendars?
This calculator uses the Gregorian calendar, which is the international standard used by almost every country today.