Date & Time Tools

Date and time tools convert between calendar formats, clock formats, and timestamps, Unix epoch, ISO-8601, 12-hour AM/PM, 24-hour military, Julian day, Gregorian date, plus time-zone math across 400+ IANA regions. A backend engineer debugging a webhook that ships epoch milliseconds to a service expecting ISO UTC can paste 1740000000 into epoch-converter, read the human date, then offset it for the receiver with timestamp-timezone-converter. This category collects 100 free browser-based tools covering epoch math, time-zone shifts, date differences, leap-year checks, and zodiac lookups. Runs client-side. No sign-up.
What you can do with Date & Time Tools

Convert between timestamp formats, paste a Unix epoch into epoch-converter or convert-unix-time-to-human-time to read it, and convert-human-time-to-unix-time to go back.
Shift times across regions, convert-time-between-timezones and convert-time-between-countries handle meeting scheduling between New York, London, and Tokyo.
Measure intervals, find-date-difference counts days between two dates, and find-time-difference counts hours and minutes.

Reach for Date & Time tools when the job is calendar math, clock math, or timestamp reshaping. If the work involves epoch parsing in a cron expression, JWT exp claim, or log timestamp, Developer Tools has the debugging utilities that pair with these. For numeric work where the date is one input among many, Math & Science covers the arithmetic side. For date-heavy CSV and JSON exports, the formatters in Data Tools run first, then these tools finish the shape.
The Date & Time toolkit

Tool
What it does
When to use

Epoch Converter
Converts Unix timestamps (seconds or milliseconds) to human-readable dates and back.
Reading 1740000000 in a Postgres row or a Stripe webhook payload.

Unix Time to Human Time
Translates a Unix timestamp into a formatted calendar date with time zone.
Making sense of a log line that prints created_at as seconds since 1970.

Human Time to Unix Time
Converts a date string into a Unix epoch integer.
Building a test fixture where an API expects expires_at as an int.

Time Zone Converter
Shifts a time between any two IANA time zones.
Scheduling a 3 PM PT standup for teammates in Berlin, São Paulo, and Sydney.

Time Between Countries
Converts a time between any two country time zones.
Checking what “10 AM in Tokyo” is for a client call booked out of New York.

Date Difference Calculator
Counts days, weeks, months, or years between two dates.
Counting the exact days between a contract signing and a 90-day renewal clause.

Day of the Week Finder
Names the weekday for any calendar date.
Answering “what day was March 3, 1987?” without a perpetual calendar.

Leap Year Checker
Tests whether a given year has 366 days under Gregorian rules.
Writing a date-parser unit test that needs a Feb 29 edge case.

12-Hour to 24-Hour Converter
Converts between AM/PM clock and 24-hour military clock.
Reformatting shift-schedule stamps from a US system for an EU payroll feed.

Countdown Timer
Counts down to a target date in days, hours, minutes, seconds.
Tracking time until a product launch or an RSVP deadline.

Age Difference Calculator
Computes the exact gap between two birthdates in years, months, and days.
Filling out a legal form that requires a precise age interval.

Zodiac Sign by Date
Returns the Western zodiac sign for any birthday.
Personalizing an email campaign by sun sign without a third-party API.

Monthly Calendar Generator
Draws a printable calendar grid for any month and year.
Printing a one-sheet wall calendar for a kid’s homework schedule.

Seconds to Time Converter
Turns a raw seconds count into HH:MM:SS.
Reading a video duration of 7342 from an FFmpeg ffprobe JSON field.

Timestamp utilities handle the machine-readable side, Unix epochs, ISO-8601 strings, Julian days. epoch-converter is the most-used entry point; convert-gregorian-date-to-julian-date and convert-julian-day-to-date cover astronomy and historical-records cases.
Time-zone and clock converters bridge the formats humans read. convert-time-between-timezones moves a time between regions; convert-12hr-to-24hr and convert-military-time-to-regular-time swap clock styles.
Calendar and date-math tools answer calendar questions. find-date-difference counts intervals, find-day-of-week names weekdays, and check-if-leap-year settles the Feb 29 question.
How to choose the right date & time tool

If the input is a raw integer like 1740000000 → start with epoch-converter.
If the goal is to schedule a meeting across two cities → convert-time-between-timezones is faster than juggling World Clock apps.
If the question is “how many days from A to B” → find-date-difference returns days, weeks, months, and years in one shot.
If the input is a video duration in seconds → convert-seconds-to-time formats it as HH:MM:SS.
If the file uses 24-hour military-style stamps and the UI expects AM/PM → convert-24hr-to-12hr handles the swap.

The trade-off worth knowing: browser tools treat time-zone data as a snapshot of the IANA tzdata version they were built against. For a one-off conversion or a date within the last 30 years, that’s fine. For dates before 1970, or DST edge cases in countries that changed rules in 2024, cross-check with a language-native library like pytz, date-fns-tz, or Luxon before it goes into production code.
Frequently asked questions
Q: What’s the difference between a Unix timestamp in seconds and milliseconds?
Seconds is the integer count since 1970-01-01 UTC (10 digits for present-day values). Milliseconds is the same count × 1000 (13 digits). JavaScript’s Date.now() returns milliseconds; most databases and the Unix date +%s command return seconds. Paste either into epoch-converter, it detects the format by digit count and converts both ways.
Q: How do I calculate the exact number of days between two dates?
Paste both dates into find-date-difference. The result shows days, weeks, months, and years in parallel, so a 90-day renewal clause and a 3-month clause can be compared side by side. For age-specific output (years + months + days), find-age-difference breaks the interval down the way legal forms want it.
Q: How do I convert a time between two time zones?
Use convert-time-between-timezones when the input is an IANA zone ID like America/New_York or Asia/Tokyo, and convert-time-between-countries when it’s a country name. Both handle DST automatically from the target date, a 3 PM New York meeting in July (EDT) and in January (EST) maps to different UTC offsets.
Q: How do I check whether a year is a leap year?
A year is a leap year if it’s divisible by 4, except century years, which must also be divisible by 400, so 2000 is a leap year, 1900 isn’t. check-if-leap-year applies the Gregorian rule. find-leap-years lists every leap year in a range, useful for generating test data.
Q: How do I convert military time to regular time?
Paste the 24-hour value into convert-military-time-to-regular-time. 1400 becomes 2:00 PM; 0030 becomes 12:30 AM. For the reverse direction, convert-regular-time-to-military-time takes 6:45 PM and returns 1845. Both accept input with or without the colon separator.
Q: Can I find out what day of the week a historical date fell on?
Yes. find-day-of-week accepts any Gregorian date from year 1 onward and returns the weekday. For dates before the Gregorian calendar’s 1582 adoption, the result is the proleptic Gregorian weekday, the calendar in use today, projected backward. Julian-calendar weekdays need a pass through convert-gregorian-date-to-julian-date first.
Related categories
Developer Tools include cron parsers, JWT decoders, and curl-to-fetch translators, the utilities a backend engineer pairs with epoch converters. Math & Science covers numeric operations when the date is one input in a larger calculation. For date-heavy CSV and JSON exports, start with the formatters in Data Tools first.