Date Calculator
Calculate date intervals and business days, or add and subtract days, weeks, months and years. Everything runs locally in your browser — no sign-up and no data upload.
Free Online Date Calculator
DevTools Date Calculator is a free online tool that answers the most common date questions in seconds: how many days are between two dates, how many business days fall in that period, and what date you get after adding or subtracting a number of days, weeks, months or years. Whether you are planning a project, calculating an age, counting down to an event or checking a contract deadline, you no longer need to count on a paper calendar — the tool handles the math, including leap years and months with different lengths, and always returns the exact result.
There is nothing to install and no account to create. The tool works directly in your web browser on desktop and mobile. All dates you enter stay on your device and are processed locally with JavaScript; they are never uploaded to a server, which makes the calculator fast and completely private to use.
What the Date Calculator can do
Days between two dates
Pick a start and an end date to instantly see the interval expressed in days, weeks, months and years, plus the total hours and minutes.
Business days counter
The result includes a business-days count that automatically excludes Saturdays and Sundays, useful for project timelines and service-level agreements.
Add or subtract time
Choose a base date and add or subtract any number of days, weeks, months or years to find the target date — for example, 90 days from today or 6 months before a deadline.
Leap year aware
Month and year calculations follow the real calendar: February gets 29 days in leap years, and adding months keeps the correct calendar day where possible.
One-click copy
Every result number and the calculated target date can be copied to the clipboard with a single click, ready to paste into an email, spreadsheet or document.
Private by design
No forms, no sign-up and no server requests. Your dates never leave your browser, so you can safely work with personal or business deadlines.
How to calculate the days between two dates
- Open the Date Interval tab and choose a start date and an end date using the date pickers (or click "Today" to fill in the current date).
- The result updates automatically: review the total days, weeks, months, years, hours and minutes, and the number of business days between the two dates.
- Switch to the Add / Subtract tab to pick a base date, enter a number, choose days, weeks, months or years, and read the resulting target date. Click any result to copy it.
Common uses
- Project planning: estimate durations and count business days available in a sprint.
- Age calculation: find out exactly how many days, months or years old someone is.
- Contract and warranty deadlines: check expiry dates and renewal windows.
- Event countdowns: see how many days remain until a wedding, vacation or launch.
- Finance and billing: calculate interest periods, payment terms and due dates.
- HR and leave: count working days and compute return dates from leave start dates.
Frequently asked questions
How do I calculate the number of days between two dates?
Open the Date Interval tab, select a start date and an end date, and the tool immediately shows the total number of days between them. The result also breaks the interval down into weeks, months and years, and reports the number of business days.
Does the calculator account for leap years?
Yes. All calculations use your browser’s real calendar, so February has 29 days in leap years and the difference between dates spanning a leap year is counted correctly.
What is the difference between calendar days and business days?
Calendar days count every day from the start date to the end date, including weekends. Business days (working days) count only Monday to Friday and exclude Saturdays and Sundays. The calculator shows both figures.
Can I add or subtract months and years, not just days?
Yes. In the Add / Subtract tab you can choose days, weeks, months or years. When adding months, the tool follows calendar months — for example, January 31 plus one month resolves to the last valid day of February.
Is the date calculator free to use?
Completely free. There is no usage limit, no registration and no payment required. You can use the date calculator as often as you like on desktop or mobile.
Are the dates I enter uploaded or stored?
No. The tool runs entirely in your browser using JavaScript. The dates you select never leave your device and are not stored on any server.
Understanding date calculations
At its simplest, a date difference is computed by converting both dates to a timestamp (the number of milliseconds since the Unix epoch on January 1, 1970), subtracting one from the other, and dividing the result by the length of a day — 86,400,000 milliseconds. This gives an exact day count that automatically handles months of different lengths and leap years.
Converting days into weeks, months or years is an approximation because months and years are not fixed lengths: an average month is about 30.44 days and an average year about 365.25 days. For legal, financial or payroll purposes, always state the exact calendar days and use month or year figures only as a human-friendly summary.
Business-day calculations walk through the calendar one day at a time and count only Mondays through Fridays, skipping weekends. Note that this tool does not subtract public holidays, because holiday schedules differ by country and region; subtract those manually if your use case requires them.
Adding and subtracting dates follows calendar semantics rather than fixed day counts. Adding one month to January 15 gives February 15, while adding one month to a day that does not exist in the target month (such as March 31 plus one month) lands on the last valid day of that month. This mirrors how people intuitively reason about deadlines like "three months from today".
Related time and date tools
- Timestamp converter — convert between Unix timestamps and human-readable dates
- Timezone converter — compare and convert times across world time zones
- Cron expression generator — build and schedule recurring tasks
- Stopwatch — an online millisecond-precision timer
Tip: this calculator works fully offline once the page has loaded, and none of your input is sent over the network.