THE TIME TOOLS YOU NEED

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All time and date tools

25 free calculators and clocks, plus 29 city time pages and 22 time-difference comparisons — grouped by the question they answer.

Clocks and time zones

For anything that crosses a border: what time it is somewhere else, when a call works for everyone, and when a plane actually lands. Every one of these uses the IANA time zone database, so daylight saving changes are applied for the exact date you enter, not today's offset.

LIVE

Local Zone Time & World Clock

Your exact local time, 28 live city clocks and a 110-city directory with UTC offsets and weather.

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CONVERT

Time Zone Converter

Convert a date and time between any two zones, including the date change when you cross midnight.

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PLAN

Meeting Planner

Line up working hours in up to five cities and see the overlap highlighted.

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TRAVEL

Flight Arrival Calculator

Departure time plus flight length gives your local landing time — date line and DST included.

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DEVELOPER

Unix Timestamp Converter

Turn epoch seconds or milliseconds into a readable date, or a date into a timestamp.

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EMBED

Embeddable Clock Widget

Generate a live clock for any city and paste it into your own website.

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Date and calendar calculators

Date math is where most mistakes happen — month lengths, leap years, whether the end date counts. These calculators show their working and say which convention they use, so you can check a result instead of just trusting it.

DATES

Date Calculator

Days between two dates, or add and subtract days from any date. Shareable result links.

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WORK

Business Days Calculator

Count working days between dates or add them to a deadline, with custom weekends and U.S. holidays.

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AGE

Age Calculator

Exact age in years, months and days, plus total days lived and the next birthday.

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AGE GAP

Age Difference Calculator

The exact gap between two birthdays or any two dates.

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WEEKDAY

Born on What Day

Find the weekday for any birth date, and which weekday your birthday falls on this year.

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ISO 8601

ISO Week Number

Today's ISO 8601 week with its Monday–Sunday range, plus a lookup for any date.

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CALENDAR

Calendar & Reminders

A simple calendar with recurring events and email or browser reminders.

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Timers and countdowns

Live timers that keep accurate time even when you switch tabs.

COUNTDOWN

Countdown Timer

Count down to any date and time, and share the countdown with a link.

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SEASONAL

Days Until Christmas

A live countdown to 25 December, plus Thanksgiving, Black Friday and Christmas Eve.

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TIMER

Online Stopwatch

A large, accurate stopwatch with lap times that survives tab switches.

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Planning your day

Tools for the time you actually have: sleep, commitments and routines. Everything you enter stays in your browser.

SLEEP

Bedtime Calculator

Bed and wake-up times based on 90-minute sleep cycles.

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TODAY

Busy Score

Add up today's meetings and commitments to get a 0–100 read on how full your day is.

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AUDIT

Daily Time Audit

Split your 24 hours into categories and see how much time is genuinely unclaimed.

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ROUTINE

Routine Builder

Build a routine block by block on a 24-hour timeline and spot gaps and overlaps.

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HABITS

Habit Clock

Short timed habit sessions with a daily streak.

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Daily extras

Small things that change every day.

DAILY

Daily Briefing

Today's hottest and coldest cities, longest and shortest days, moon phase and upcoming clock changes.

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DAILY

Time Zone Fact of the Day

A new fact about odd offsets, date-line jumps and how standard time came about.

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GAME

Daily Time Puzzle

Guess the local time in a mystery city and build a streak.

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WEATHER

Local Weather

Current conditions, hourly outlook and 7-day forecast for any city.

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Current time by city

Each city page has a live clock, the city's daylight saving dates, sunrise and sunset, the best hours to call from other regions, and a short history of how the city came to keep the time it does.

Time differences between cities

Side-by-side comparisons for city pairs that people schedule between most often, including how the gap changes when only one side observes daylight saving.

How these tools work

Every clock and converter on WatchTime Online runs in your browser. Times come from your device clock, and time zone rules come from the IANA time zone database built into modern browsers — the same database used by operating systems and airline booking systems. That's why the converter knows that London moves to summer time on a different weekend than New York, and why a calculation for a date next March uses next March's offset rather than today's.

Nothing you type into a calculator is sent to a server. The two exceptions are the weather pages, which ask Open-Meteo for a forecast, and the calendar, which stores events so it can send reminders. Both are explained in the privacy policy.

If you'd like the reasoning behind the numbers — why some years have 53 ISO weeks, or why there are more than 24 time zones — the guides cover the rules in plain English. Found a result that looks wrong? Tell me and I'll check it.