Days Between Dates Calculator
Count the days, weeks, and approximate months between any two dates — handy for trip planning, deadlines, and milestones.
Days
365
Weeks
52.14
≈ Months
12.0
Formula
Days = (End date − Start date) in calendar days
Worked example
From 2025-01-01 to 2026-01-01.
- 2025 is not a leap year, so it contains 365 days.
- Difference = 365 days = ~52.14 weeks ≈ 12 months.
Answer: 365 days
How it works
The calculator subtracts the two calendar dates and reports the gap in days. Weeks are simply days ÷ 7, and months use 30.4375 days as the average month length so they line up with a full year of 365.25 days.
Months are an approximation because real months range from 28 to 31 days. For things like a contract that runs in calendar months, prefer the months figure as a rough guide rather than an exact count.
If the end date is earlier than the start date, the calculator shows the absolute difference and notes the order so you don't get a confusing negative.
Under the hood the tool converts both dates to UTC midnight before measuring the gap. Because UTC never observes daylight saving time, the result stays the same even if a spring-forward or fall-back transition falls between your dates. See the developer note in the source code (src/lib/formulas.ts) for the full details.
Common mistakes
- Including or excluding the start day when counting — the calculator uses end minus start, so a one-day gap returns 1.
- Using the approximate months value as if it were exact months on the calendar.
- Entering a non-existent date like Feb 30 or April 31; the validator will reject it.
FAQ
- Is the end date included?
- We compute end minus start, so the start day isn't counted and the end day is the last day in the span.
- What if the end date is before the start?
- We show the absolute difference and flag that the end date is before the start date.
- Why is the months figure not a whole number?
- Months vary between 28 and 31 days. We divide by the average (30.4375), so most spans land on a decimal.
- Does it count leap days?
- Yes — leap days are part of the calendar difference whenever they fall between your two dates.
- How can I count business days only?
- This tool counts every calendar day. For working days only you'd need to subtract weekends and holidays manually.