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. 31 Jan + 1 month → 28/29 Feb) and leap years. For business-day-only math (excluding weekends and holidays), use the business days calculator — this tool counts calendar days unless you specify otherwise.
Base date (YYYY-MM-DD)
Days to add (negative to subtract)
Result
2026-09-11
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.
When to choose something else
• When only business days count — use the business days calculator.
• When you need the span between two dates — use days between dates.
• When legal deadlines follow court rules (holiday calendars) — verify officially.
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.
Month-end pitfalls in contracts
“One month from 30 January” might mean 28 February or 30 March depending on jurisdiction and drafting. Software typically preserves day-of-month or clamps. For high-stakes notices (lease termination, regulatory filings), cite the explicit calendar date in writing rather than relying on relative month arithmetic alone.
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.
Is my data sent to a server?
No.
Is this tool free?
Yes.