About this site

What this site is

DateAndTimeCalculator.org provides 15 calculators for date differences, working days, time durations, ages, deadlines, time zones and Unix timestamps. Everything is free, works without an account, and works on a phone.

How the calculations are produced

Every calculator is built on the same tested calculation library, which is covered by an automated test suite that runs against known edge cases: leap years, month ends, daylight-saving transitions, shifts crossing midnight, negative durations, invalid input and published holiday dates. The tests exist so that a later change cannot silently alter a result.

Three decisions underpin the whole site:

• Dates are calculated in whole days, not clock time. Local-time arithmetic loses or gains an hour at daylight-saving transitions, which turns "add one day" into "add 23 hours" twice a year. All date maths runs on UTC-based day counts, where every day is exactly the same length.
• Times are held as minutes past midnight. This makes a shift crossing midnight ordinary arithmetic rather than a special case, and means a clock change can never alter someone's recorded hours.
• Ambiguity is shown, not hidden. Where two reasonable conventions exist, the page says which one it used and lets you change it where sensible.

Where the data comes from

Public holidays

Holidays for 13 countries and territories are computed from their published rules — fixed dates, nth-weekday rules, and offsets from Easter — rather than stored as a fixed table that expires. The one exception is New Zealand's Matariki, which is set by observation rather than by a rule, so only officially gazetted dates are listed and the limits are stated on the page.

These are national holidays only. Regional, state, provincial and company holidays are not included. The calendar was last reviewed on 30 July 2026.

Time zones

Time zone rules come from the IANA time zone database built into your browser — the same source used by operating systems and most programming languages. Because the data comes from your device rather than from this site, it stays current with rule changes as your browser updates.

Calendar

The proleptic Gregorian calendar is used throughout, including for dates before its adoption in any particular country. Week numbers follow ISO 8601. Historical dates before the eighteenth century may not match contemporary records, which often used the Julian calendar.

What this site is not

This site provides general calculation tools. It is not a legal, payroll, financial, tax, medical or immigration advisory service, and no result should be treated as professional advice.

Where a date carries a legal or contractual consequence — a statutory deadline, a notice period, a limitation date, a filing deadline, an entitlement calculation — confirm the result against the relevant official source and the wording of the agreement. Counting rules vary, and the difference between "days" and "working days", or between including and excluding the first day, is frequently decisive.

Corrections

If a result looks wrong, we want to know. Accuracy is the only thing this site has to offer, and a reproducible bug report — the inputs, the result you got, and the result you expected — is the most useful thing you can send. Get in touch through the contact page.

How the site is funded

The site is supported by advertising. Adverts are placed below results and between sections of supporting text — never between form fields, beside the Calculate button, or over a result. The calculators work identically when adverts are blocked, and no advert is ever allowed to load before the calculation it sits beneath.

Advertising uses cookies, so nothing is stored until you have agreed to it, and you can change your answer at any time using the Cookie settings link in the footer. Any analytics used here are cookieless and aggregate-only, chosen so that measuring which calculators are useful does not require tracking anybody. See the privacy policy and cookie policy for the detail.