Date Calculator
Calculate date differences and add/subtract days
Date Calculator tool
Date Calculator: key facts
- What it does
- Calculate date differences and add/subtract days
- Category
- Other Calculators
- Cost
- Free, with no account, sign-up, or install.
- Your data
- Runs entirely in your browser — the files and text you enter are never uploaded to a server.
- Last reviewed
- . Report an incorrect result.
Understanding the Date Calculator
Counting the days between two dates by hand means wrestling with month lengths and leap years, and it is easy to be off by one. This calculator takes a start and end date and tells you the span in days, weeks, months, and years — and can count only working days when weekends should not count.
People use it to find how many days until a deadline, how long ago something happened, or how many business days a project window actually contains. The working-days option is what sets it apart for anyone planning around a Monday-to-Friday schedule, and an "include end date" toggle handles whether the final day counts.
Getting a result
- Pick the start date.
- Pick the end date (use the swap button if you entered them in the wrong order).
- Toggle "include end date" if the final day should count, and "working days only" to exclude weekends.
- Read the span in days, weeks, months, and years, plus the working-day count when enabled.
Days, weeks, months, years, and working days
The span between two dates is computed by normalising both to midnight and taking the difference in days — normalising first is what stops a time-of-day component producing an off-by-one result. Weeks follow by dividing by seven.
Months and years are counted from the calendar rather than from an average month length. The month figure comes from the difference in years and months, minus one where the day of the month has not yet come round, and years are derived from that. Counting this way is what makes an exact anniversary report twelve months and one year rather than being lost to a fractional average.
Working days are counted by stepping through the range and skipping Saturdays and Sundays, so the figure reflects actual weekday count rather than an estimate from the total.
- 1 January 2025 to 1 January 2026 is 365 days, 52 weeks, 12 months, and 1 year.
- 1 January to 1 July 2025 is 181 days and 6 months.
- 29 February 2024 to 28 February 2025 is 365 days but 11 months, because the day of the month has not quite come round.
Reasons to use it here
- It can count working days only, excluding Saturdays and Sundays — useful for business and project timelines, not just raw calendar days.
- It expresses the gap four ways at once (days, weeks, months, years), so you get the unit you need without extra math.
- An "include end date" toggle and a swap button handle the off-by-one and wrong-order mistakes that trip up manual counting.
- It works entirely in your browser, so your dates stay private.
Inclusive counting, and the calendar's irregularities
Whether to count both endpoints is a real ambiguity rather than a detail, which is why it is an option. Asked how many days a hotel stay covers, most people mean nights — the exclusive count. Asked how many days a festival runs, they mean the inclusive count including both the first and last. Contractual and legal deadlines have their own conventions, and getting this wrong by one day has consequences.
Months are the awkward unit because they have no fixed length. A month from 31 January is genuinely ambiguous, since there is no 31 February, and different systems resolve it differently — some clamp to the last day of the month, others roll into March. Any month arithmetic carries an assumption somewhere.
The working-day count here skips weekends only. Public holidays are not deducted, and they vary by country, region, and year, so a business-day figure for a deadline should be checked against the relevant holiday calendar. Note too that not every part of the world treats Saturday and Sunday as the weekend.
Frequently Asked Questions
Does the calculation include both the start and end dates?
By default it counts the gap between the dates, not the end date itself. Turn on "include end date" to count the final day too — useful when you want the total number of days in a range rather than the difference between them.
How are working days counted?
With "working days only" enabled, the calculator steps through each day in the range and counts only Mondays through Fridays, skipping weekends. Note that it does not account for public holidays, which vary by country and region.
Why might the months figure look approximate?
Months vary in length, so the calculator derives months from the total day count using an average year length. For exact calendar-month differences, the day count is the most precise figure to rely on.
Can I count down to a future event?
This calculator measures the span between two chosen dates. To count down to an event, set the start to today and the end to the event date; the day count tells you how long remains, and the working-days option shows the business days left.
