Date Difference Calculator
Find the number of days, weeks, months, years (and more) between two dates
How this calculator works
Enter a start date and an end date to compute the day difference using date-only math (no time-of-day). The calculator provides multiple units:
- Total days - exact number of calendar days
- Weeks + days - breakdown into whole weeks and remaining days
- Total months/years - approximate conversions using averages
- Decades/centuries - shown when applicable (10+ or 100+ years)
Common use cases
Project timelines
Calculate days between milestones or delivery dates.
Legal deadlines
Count days for filing periods, statutes of limitations.
Historical research
How many years/decades between historical events?
Billing cycles
Days in a billing period for invoicing or subscriptions.
Units explained
| Unit | Based on | Notes |
|---|---|---|
| Days | Exact count | Primary result, always accurate |
| Weeks | 7 days | Exact (days / 7) |
| Months | 30.44 days avg | Approximate (365.25 / 12) |
| Years | 365.25 days | Accounts for leap years |
| Decades | 10 years | Shown when 10+ years |
| Centuries | 100 years | Shown when 100+ years |
Examples
Jan 1 to Jan 2
Default: 1 day. With "include end date": 2 days.
End before start
With absolute difference ON, dates are swapped internally.
Feb 5, 1822 to Feb 6, 2026
74,425 days = 203.77 years = 20.38 decades = 2.04 centuries
90 days in months
90 days = 2.96 months (based on 30.44 avg)
Frequently Asked Questions
What does "include end date" mean?▼
If enabled, the count includes the end date itself. For example, Jan 1 to Jan 2 becomes 2 days instead of 1. Useful when counting "days in a period" rather than "days between".
What does "absolute difference" mean?▼
If enabled, the calculator always returns a positive day count by treating the dates as unordered. Useful when you just want the gap regardless of which date is earlier.
Why do some calculators differ by one day?▼
Differences often come from inclusive vs exclusive counting, or mixing timestamps with date-only values. This tool uses date-only, UTC-midday math to avoid timezone and DST drift.
Does this include time of day?▼
No. This is a date-only calculation (YYYY-MM-DD) and ignores hours/minutes. For time-aware calculations, use a datetime difference tool.
How are months and years calculated?▼
Months use an average of 30.44 days (365.25 / 12), and years use 365.25 days (accounting for leap years). These are approximations; for exact calendar months, use a specialized tool.
When do decades and centuries appear?▼
Decades appear when the difference is 10+ years, and centuries appear when it's 100+ years. They're based on the same 365.25 days/year average.
How do I calculate business days instead?▼
This calculator counts calendar days (including weekends). For business days only (excluding weekends and holidays), use a dedicated business days calculator.
Can I use this for age calculation?▼
For a quick approximation, yes. For precise age with years/months/days breakdown and birthday countdowns, use the dedicated Age Calculator.