Tip: Everything runs locally in your browser.
Converter Result
Converter Result
Select a mode and fill the form. Click Calculate to see results here.
Total Days:
Total Weeks:
Calendar Y/M/D Breakdown:
Target Date:
Weekday:
ISO Date:
Calculation Principles & Formulas
The Date Interval Calculator operates in two modes: 1. Date Difference: Calculates the total time span (years, months, days) between two dates. 2. Add/Subtract Interval: Calculates a target date by adding or subtracting years, months, weeks, or days from a start date.
[Formulas]
1. Date Difference (A - B):
Total Days = (End Date - Start Date in ms) / 86,400,000
Breakdown: Calculated sequentially (Full Years → Full Months → Remaining Days).
(If 'Include end date' is checked, Total Days + 1)
2. Add/Subtract Interval:
Target Date = Start Date + (Years × 12 + Months) months + (Weeks × 7 + Days) days
Note: Month additions handle varying days in months and leap years (e.g., Jan 31 + 1 month = Feb 28 or 29).
Note: All calculations follow the Gregorian calendar rules.
How to Use
- Select calculation mode: Date Difference (interval between two dates) or Add/Subtract Interval (modify a base date).
- In Date Difference mode, pick start and end dates, toggle 'Include end date', and click 'Calculate'.
- In Add/Subtract mode, set the base date and input years/months/weeks/days to add (use negative numbers to subtract).
- View results including total days, total weeks, Y/M/D breakdown, or the target date and weekday.
- Click the copy icon next to any result to copy it to your clipboard.
Tips
- Handles leap years and varying month lengths automatically.
- In Add/Subtract mode, use negative numbers to calculate past dates.
- All calculations are performed locally in your browser. No data is uploaded to any server.
