Add or subtract days from a date, or find the number of days between two dates.
Frequently Asked Questions
How do I add days to a date?
Enter your start date, choose Add, enter the number of days, and the calculator returns the resulting date, including the day of the week.
How do I find the number of days between two dates?
Enter both dates in the "Days Between Dates" tab. The calculator subtracts the earlier date from the later one and shows the total days and weeks.
Does this calculator account for leap years?
Yes, all date math uses real calendar dates, so leap years are handled automatically.
How date calculations work
The add/subtract mode moves forward or backward a set number of calendar days from your start date and reports the resulting date and day of the week. The days-between mode subtracts one date from another to find the total number of days (and weeks) separating them, correctly accounting for leap years.
How to use this date calculator (days between dates)
- Choose add/subtract days, or days between two dates.
- Enter your date(s) and, if applicable, the number of days.
- Click Calculate.
Why date math needs a calculator
Months have different numbers of days, leap years add an extra day roughly every four years, and manually counting weeks or days across several months is error-prone. This calculator handles all of that automatically using real calendar dates, so „90 days from March 15“ or „how many days between two project deadlines“ comes out correct without manual counting.
Common uses for a date calculator
- Deadlines and due dates: Finding the exact date a set number of days from now, such as a 30-day return window or a 90-day notice period.
- Countdowns: Finding how many days remain until an event, trip, or deadline.
- Contract and legal terms: Many contracts specify obligations in days rather than months, where precise day counts matter.
- Age and anniversaries: Calculating days since a specific date, such as a start date, wedding, or anniversary.
Tips for working with date calculations
Be clear about whether „30 days from today“ should include or exclude the starting day — conventions differ between contracts, so check the exact wording if the count is legally or financially significant. When working across time zones, remember this calculator uses calendar dates only and does not adjust for time zone differences.
Expert insight: date math gets surprisingly technical for professionals
Professional genealogists, who calculate dates for a living when historical records are incomplete, follow a strict protocol from the Board for Certification of Genealogists: state your calculation method consistently and never quietly adjust a date to make the numbers look neater. For anyone working with historical dates before the early 1900s, they also flag a genuinely tricky wrinkle this calculator doesn’t need to worry about — different countries switched from the Julian to the Gregorian calendar in different years, so historical date gaps aren’t always what a modern calculation would suggest.
Further reading: Your 2026 Tax Deadlines at a Glance — And Why Exact Date Math Matters
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Disclaimer: This calculator is provided for general informational and educational purposes only and does not constitute financial, investment, tax, or legal advice. Results are estimates based on the values you enter and should not be relied upon as the sole basis for any financial or other decision. Past performance and projected figures are not a guarantee of future results. Always consult a qualified professional before making financial decisions. See our Legal Notice and Privacy Policy for more information.