Date Validator
Use this free Date Validator to quickly get accurate results in seconds, free and instantly offline with no signup required ever, trusted by professionals in Austin, Chicago, Miami, Denver, Seattle, and New York for reliable daily use without accounts, subscriptions, limits, or delays on any device for everyday personal and business workflows daily.
Check dates with this date validator, validating day, month, and year format, calendar correctness, and leap years for date inputs.
Calculator Inputs
About Date Validator
Use this free Date Validator to quickly get accurate results in seconds, free and instantly offline with no signup required ever, trusted by professionals in Austin, Chicago, Miami, Denver, Seattle, and New York for reliable daily use without accounts, subscriptions, limits, or delays on any device for everyday personal and business workflows daily.
Calendar Correctness: A date is only valid if the day exists in that specific month and year — 30 February never exists, and 29 February only exists in leap years (divisible by 4, except centuries not divisible by 400). This validator enforces the actual Gregorian calendar rules, not just regex patterns.
Dual Format Support: Accepts ISO 8601 (YYYY-MM-DD or YYYY/MM/DD) and day-first (DD/MM/YYYY or DD-MM-YYYY). Two-digit years (DD/MM/YY) are interpreted as 2000–2099. Other layouts are rejected as unsupported rather than misparsed.
Leap Year Precision: 2000 was a leap year (century divisible by 400). 1900 was not (century not divisible by 400). 2024, 2028, 2032 are leap years. The tool applies the full rule: (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0. No shortcuts, no approximations.
Output Normalization: Valid dates return the ISO 8601 format (YYYY-MM-DD), the weekday name (Monday–Sunday), and parsed components. This makes output directly usable in databases, APIs, and other tools without re-parsing.
Privacy & Speed: Validation is pure arithmetic — no Date object quirks, no timezone ambiguity, no network. Runs in microseconds entirely in your browser. Safe for PII-adjacent workflows where date strings must not leave the client.
Where it is used
A form developer in Austin testing date picker edge cases; a data analyst in Chicago cleaning CSV imports; a travel app dev in Miami validating booking dates; a compliance officer in Denver checking filing deadlines; a scheduling tool builder in Seattle handling recurring events; a tax preparer in New York verifying quarter-end dates.
How to use the Date Validator
- Date string — enter the value (e.g. 2026-02-29 or 31/12/2025).
- Calculate — press the Calculate button to see the result instantly above.
Formula
ISO (YYYY-MM-DD) or DD/MM/YYYY → Gregorian calendar check + leap year rules → weekday.
Examples
Leap Day Valid
Leap Day Invalid
Day-First Format
Frequently Asked Questions
- What formats do you accept?
- ISO (YYYY-MM-DD or YYYY/MM/DD) and day-first (DD/MM/YYYY or DD-MM-YYYY). Two-digit years become 2000–2099. Other layouts (MM/DD/YYYY, YYYY.MM.DD, etc.) are reported as unsupported.
- Are leap years handled correctly?
- Yes — full Gregorian rule: divisible by 4, except centuries not divisible by 400. So 2000 was leap, 1900 was not, 2100 will not be. February 29 only passes in true leap years.
- Does it handle timezones?
- No — this validates calendar dates only (year, month, day). Time components and timezones are ignored. For datetime validation, use a dedicated datetime parser.
- What about dates before 1582 (Gregorian adoption)?
- The tool applies Gregorian rules proleptically (extended backward). Historical dates before 1582-10-15 used Julian calendar in most countries — results may not match historical records.
- Can it validate "31/04/2026" (31 April)?
- No — April has 30 days. The tool catches this and returns invalid. Same for 31 June, 31 September, 31 November.
- Is my date string stored?
- Never. Validation is pure client-side logic. No network, no logs, no analytics. Works offline.