About Date Difference
Calendar difference between two dates. Days, weeks, months, years with leap-year handling. Add or subtract intervals from a date. Useful for project planning, anniversary calculations, and account-age math.
When this beats a calendar app
- Project deadlines: “How many days from kickoff to launch?”
- SLA math: “Account opened on X, support ticket on Y, time to issue?”
- Anniversaries: “Wedding on June 14 — what is the 25th anniversary date?”
- Invoice aging: “Invoice issued 47 days ago, due in 13 days.”
Common workflows
Add a notice period. Today + 60 days = end-of-notice date.
Find an anniversary. Wedding date + 25 years = silver anniversary.
Project span. Start to end → months and weeks for status meetings.
Visa expiry. Issue + 12 months = expiry. Pin to your calendar.
Frequently asked questions
How is "months" calculated?
Calendar months — Jan 15 to Feb 15 is 1 month, even though it could be 28-31 days. We step month by month.
Inclusive or exclusive endpoints?
Toggle. Default is exclusive (Jan 1 to Jan 5 = 4 days). Inclusive counts both ends (= 5 days).
Add or subtract days from a date?
Toggle to Add mode. Pick a date, an interval (days, weeks, months, years), get the resulting date.
Business days only?
Use the Workday Calculator for business-day counts. This tool counts all days.
Cross-timezone math?
Same timezone (your local) for both dates. For cross-zone, convert with Timezone Converter first.
How does it handle leap years?
Day count is exact across leap days. Year count uses the anniversary rule — Feb 29 anniversary lands on Feb 28 in non-leap years.
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Last updated: 2025-01-15