Two dates — days, weeks, months, years between them. Bonus: age from birthdate + days until next birthday.
Runs entirely in your browser. Your data never leaves your device.
Difference in days is computed using the UTC day numbers (ignoring local time zones), so DST transitions never affect the count. Calendar-aware months/years are computed by iterating whole months and then adding a remainder in days.
| Metric | How |
|---|---|
| Days | (UTC(dateTo) − UTC(dateFrom)) / 86,400,000 |
| Weeks | floor(days / 7) |
| Months | Calendar-aware: count whole months, remainder in days |
| Years | Whole calendar years, remainder in months/days |
| From → To | Days | Years · Months · Days |
|---|---|---|
| 2024-01-01 → 2025-01-01 | 366 (leap year) | 1 · 0 · 0 |
| 2024-02-28 → 2024-03-01 | 2 | 0 · 0 · 2 |
| 2023-06-15 → 2026-09-23 | 1166 | 3 · 3 · 8 |
Manually verified. Last checked: September 2026.
Days are exact (86,400 seconds). Months and years use calendar-aware math — the difference is computed by counting whole calendar months/years first, then expressing any remainder in days. This handles leap years and varying month lengths correctly.
Because weeks are a handy mid-unit between days and months. Total days ÷ 7 gives you the total weeks between two dates, regardless of month boundaries.
No. All calculations run locally in your browser. No dates or birthdates you enter are transmitted anywhere.
Total Days goes negative, and the result shows the absolute value in parentheses right next to it, so a swapped pair of dates is easy to spot. Weeks, months and years follow the same sign.
This page includes a bonus age section, so either one works for a plain age. Reach for the Age Calculator when the birthdate is the whole point: it adds weeks and hours lived plus the Chinese and Western zodiac signs.
Once you know the span, plan with it: step a set number of days forward in the Date Adder and look up the sign of either date in the Chinese Zodiac Calculator.
If you just finished with Date Difference Calculator, the natural next steps are Date & Time Formatter, FIRE Retirement Calculator, Time Zone Converter, or browse every tool in Daily Tools.