Date Difference Calculator
Total days, weeks, and months between any two calendar dates.
What it does
Date difference counts whole days between two calendar dates. Trip planners use it for night counts, contracts use it for notice periods, and countdowns use it for the wait itself, all from the same subtraction.
The tool above takes a start and an end date. It returns total days, decimal weeks, and average months side by side, with both weekday names in the note for orientation.
The default spans Jan 1 to Mar 1 2026: 31 days of January plus 28 of February 2026 for 59 days total, about 8.4 weeks or 1.9 average months. February 2026 has 28 days since leap years fall on multiples of four with century exceptions.
All parsing and getters run in UTC following NIST timekeeping practice, with time.gov as the public face of official US time. Local zones and daylight changes therefore cannot add or drop a day the way midnight local math sometimes does.
How to use
- Pick the start date first, such as today or a departure.
- Pick the end date, such as a deadline or return.
- Read total days first for the exact count.
- Use weeks for schedules and months for rough planning.
- Swap the dates if the page reports the end sits before the start.
Formula
- UTC noon
- Both dates parsed at 12:00 UTC to dodge zone edges.
- 86400000
- Milliseconds in one day.
- 30.436875
- Average month over a 400 year Gregorian cycle.
Same date twice reads zero days. End before start is rejected instead of returning a negative, so countdowns fail loudly rather than silently.
Worked example
Example: Jan 1 to Mar 1 2026
Start 2026-01-01, end 2026-03-01.
- January part: Jan 1 to Feb 1 is 31 days.
- February 2026 part: Feb 1 to Mar 1 is 28 days.
- Total: 31 + 28 = 59 days.
- Weeks: 59 / 7 = 8.4 weeks. Months: 59 / 30.436875 = 1.9 months.
- Tool shows 59 days, 8.4 weeks, 1.9 months.
Reference table
| Span | Days | Reads as |
|---|---|---|
| One week | 7 | 1.0 weeks |
| 30 days | 30 | about 1.0 months |
| 90 days | 90 | about 3.0 months |
| 365 days | 365 | about 12.0 months |
| 59 days here | 59 | 8.4 weeks |
Limits
- Whole days only. Hours within a day need the time duration page.
- Counts days, not business days; weekends stay included.
- Public holidays stay included and need manual subtraction.
- Average months are rough; billing months follow exact dates.
Common mistakes
- Counting both endpoints and landing one day high.
- Using local midnight math across a daylight change.
- Forgetting February length in the span years.
- Reading average months as exact billing months.
- Expecting workdays from a total days count.
Try it yourself
Quick checks. Answers sit tucked under each question.
Mar 1 to Mar 8 2026?
7 days, exactly 1.0 weeks.
Jan 1 to Jan 31 2026?
30 days, about 1.0 months.
Same date twice?
0 days. The count stops before the end date.
Questions
How many days between two dates?
Subtract start from end in whole days. Jan 1 to Mar 1 2026 is 59 days.
Is the end date included?
No. The count starts at the first date and stops before the second, so same date twice is zero.
Why UTC?
Local zones and daylight shifts can nudge midnight math by an hour. UTC noon parsing keeps every day whole.
Weekends included?
Yes. For Monday to Friday counts use the workdays page instead.
How long is an average month?
30.436875 days over the Gregorian cycle, used here only for rough month equivalents.
Date difference vs age?
This page totals days between any dates. The age page splits birth spans into years, months, and days.