Date calculator
Add or subtract days, weeks, or months from a start date to find a future or past deadline. Handles month-end rollovers (e.g.
How to add or subtract dates
1. Pick a start date (defaults to today if empty).
2. Choose add or subtract and enter the amount.
3. Select unit: days, weeks, or months.
4. Read the result date — verify month-end edge cases for contracts.
Date calculation examples
90-day return window
Purchase 12 March 2026 + 90 days → 10 June 2026 (calendar days). Retail “90 days” usually means calendar, not business days.
Subtract 6 months from 31 August 2026
Result ≈ 28 February 2027 — month arithmetic clamps to last valid day when needed.
Project milestone + 3 weeks
Kickoff 5 January 2026 + 21 days → 26 January 2026. For “15 business days”, switch to the business days calculator.
When to use this tool
• When you compute contract notice periods, warranty expiry, or visa validity.
• When you plan events by shifting a known date forward or backward.
• When you verify spreadsheet DATE formulas with a quick second opinion.
Calendar vs business days
Legal and financial terms often say “30 days” meaning calendar days unless “business” or “working” is specified. Payment terms “Net 30” from invoice date usually include weekends. Shipping SLAs may count business days only. Mixing them causes missed deadlines — confirm contract language, then pick this calculator or the business days tool accordingly.
Frequently asked questions
How are months added?
We move the same day-of-month when possible; if the target month is shorter (31 Jan + 1 month → last day of Feb), we clamp to the last valid day.
Does this exclude weekends?
Not by default — all units are calendar-based. Business days require the dedicated business days tool.
Are leap years handled?
Yes. 29 February exists in leap years; adding years/months across Feb 29 follows standard date library rules.
Can I subtract dates?
Yes — subtract days, weeks, or months to find dates in the past (e.g. “30 days ago”).
What date format is used?
ISO-style YYYY-MM-DD for clarity across locales; display may follow your browser locale.