Date Calculator
Find the years/months/weeks/days between two dates, or add or subtract years, months, weeks and days from a date to get the result date.
Input Data
Results
At a glance:The date calculator handles two common operations: finding the years, months, weeks and days between two dates (optionally including the end day), and adding or subtracting years, months, weeks and days from a date to obtain a new date. The date difference uses the month-day-aligned method (former method) to break down years/months/days, avoiding ambiguity from unequal month lengths.
Formula
Difference: compute whole years first (year = end year − start year); then adjust by month and day, borrowing from the month if the end day is smaller and from the year if the month is negative, giving (year, month, day).
totalDays = total milliseconds between the two dates / 86,400,000; weeks = totalDays / 7.
Include end day: add 1 day to the end date before computing.
Add/subtract: result = start date; result year += sign×years; month += sign×months; day += sign×(weeks×7 + days). sign is +1 (add) or −1 (subtract).
How to Use
- Choose a mode: difference between two dates, or add/subtract from a date.
- Difference: enter the start and end dates; optionally check 'Include End Day' to add 1 day.
- Add/subtract: enter the start date and the years/months/weeks/days to add or subtract, then pick add or subtract to get the result date instantly.
Case Studies
2026-01-01 to 2026-01-31 (end day excluded) → 0 yr 0 mo 4 wk 2 d (30 days)
Total days = 30; broken into 4 weeks and 2 days, with 0 years and 0 months.
If 'Include End Day' is checked, the total becomes 31 days.
2026-03-01 plus 1 month → 2026-04-01
Start 2026-03-01, choose 'Add', months = 1, rest 0.
Result date is 2026-04-01 (plain month shift, no business-day adjustment).
FAQ
Do unequal month lengths affect the year/month/day breakdown?
Yes. This calculator uses the month-day-aligned method: from the start date it advances to the same day number of the next month as one full month, counting the remaining days separately. For example 2/28→3/31 is 1 month 3 days, not simply 1 month.
What does 'Include End Day' mean?
When checked, the end day itself is also counted (total days +1). Useful when the period is inclusive of both ends, such as a rental term or a medication course.
Does add/subtract automatically exclude weekends or holidays?
This version only does calendar arithmetic and does not subtract weekends or holidays. For business-day calculations, use a business-day calculator or adjust manually.
Related Tools
References
Content reviewed by the Calculatorism editorial team. Results are for reference only; please refer to the relevant authorities for the official figures.