Time & Date calculators
Date math, age calculators, time-zone deltas, business-day counters - dated against the locales we cover.
All time & date tools
34 tools, each runs locally in your browser. Click any card to open it.
Age Calculator computes age in years/months/days from birth date, target date. Runs entirely in your browser. No login…
Age Difference Calculator takes height, weight, age, sex, activity and returns the matching age difference result. Run…
Bitcoin Halving Countdown takes token quantity, price, fees, holding period and returns the matching bitcoin halving c…
Countdown to Date takes two timestamps or a base plus delta and returns the matching countdown to date result. Runs en…
Countdown to Event takes two timestamps or a base plus delta and returns the matching countdown to event result. Runs …
Date Calculator computes date difference or future/past date from start date, end date, or duration. Runs entirely in …
Days Between Dates takes two timestamps or a base plus delta and returns the matching days between dates result. Runs …
Find the right pipe diameter from area, rainfall, and slope.
Estimate replacement cost installed by door size and features.
FSI data: 600-2200 hours to professional working. Romance: 600. Asian: 2200.
Medicare Advantage vs Original is a free us healthcare calculator that gives you a deterministic answer for medicare a…
Printer Cost per Page computes age in years/months/days from birth date, target date. Runs entirely in your browser. N…
Propane Tank Usage Calculator computes age in years/months/days from birth date, target date. Runs entirely in your br…
Running Mileage Base Calculator takes vehicle price, down payment, rate, term and returns the matching running mileage…
Seedling Start Date Calculator computes date difference or future/past date from start date, end date, or duration. Ru…
Sewing Fabric Yardage computes age in years/months/days from birth date, target date. Runs entirely in your browser. N…
Sleep Need by Age Calculator computes age in years/months/days from birth date, target date. Runs entirely in your bro…
Time Zone Converter takes two timestamps or a base plus delta and returns the matching time zone result. Runs entirely…
Voltage Divider Calculator takes string, regex, format, count and returns the matching voltage divider result. Runs en…
Working Days Calculator takes two timestamps or a base plus delta and returns the matching working days result. Runs e…
⏱️ Stopwatch takes two timestamps or a base plus delta and returns the matching ⏱️ stopwatch result. Runs entirely in …
⏳ Countdown to Date takes two timestamps or a base plus delta and returns the matching ⏳ countdown to date result. Run…
🌍 World Clock takes two timestamps or a base plus delta and returns the matching 🌍 world clock result. Runs entirely…
🎂 Age Math Drill takes game state, settings, opponent profile and returns the matching 🎂 age math drill result. Runs…
Age in Days, Weeks, Months Calculator is a free everyday utility calculator that gives you a deterministic answer for …
Add Days to Date Calculator computes date difference or future/past date from start date, end date, or duration. Runs …
age in days, days alive, exact age days, lifespan in days age in days only calculator free 3tej calculator
age in months, infant age, decimal years, calendar months age in months only calculator free 3tej calculator
age in hours, heartbeats lifetime, total minutes alive, sleep hours age in hours calculator (+ heartbeats) free 3tej c…
Age in Weeks Calculator takes two timestamps or a base plus delta and returns the matching age in weeks result. Runs e…
decimal age, actuarial age, pediatric growth chart, pet age conversion age in decimal years calculator free 3tej calcu…
age difference, spouse age gap, sibling spacing, romeo juliet laws age difference between two people calculator free 3…
Calculate your weighted average cost basis when you accumulate shares through multiple purchases at different prices. …
Check whether any year is a Gregorian leap year. Returns yes or no with a clear explanation of the divisibility rules.
About time & date
Time and date calculators cover the calendar math we run for birthdays, contracts, planning, and travel: age in years/months/days, date difference, days between two dates, business days excluding weekends and holidays, countdown to a target date, world clock and timezone conversion across 70+ cities, week-number and day-of-year, leap year check, Julian date, ISO 8601 formatting, and Pomodoro session timing.
Use these to compute exact age in years/months/days/hours, count business days for a contract closing, find the day of the week for a future date, convert 3 PM London to local time across 5 cities, count down to a wedding or product launch, or sanity-check a leap year.
Sources: ISO 8601 calendar standard, IANA timezone database (regularly updated for DST and offset changes), country-specific public holiday lists where business-day calculations apply. Defaults to ISO Monday-start week; toggle US Sunday-start where the tool exposes it.
Common use cases
Real scenarios where the time & date calculators in this category earn their keep.
Exact age in years/months/days
From birthday to today (or a target date) decomposed into years + months + days, plus total days. Useful for age-related cutoffs (Medicare 65, RMD 73).
Business days between two dates
Excludes weekends and (optionally) public holidays for a country. Used for contract closings, SLA timing, and project planning.
World clock for a meeting
Pick a base time and city; the tool shows the equivalent in 5 other cities accounting for DST. Highlights cells outside business hours.
Countdown to a target
Days, hours, minutes remaining to any future date. Useful for product launches, weddings, and birthdays.
Pomodoro session planner
25-minute focus + 5-minute break, with a 30-minute long break after 4 cycles. The Pomodoro tool tracks the cycle and rings a browser notification.
Key terms
Glossary for the formulas and conventions these tools use.
- ISO 8601
- International date and time standard. YYYY-MM-DD for dates, T separator, hh:mm:ss for time, +hh:mm or Z for offset.
- Week number
- ISO 8601 week. Monday-start, first week is the one containing the first Thursday. Differs from US convention (Sunday-start, first week contains January 1).
- Leap year
- Divisible by 4, except century years which must also be divisible by 400. 2000 was a leap year; 1900 was not.
- Julian date
- Day count since 4713 BC noon UT. Used in astronomy for ephemeris calculations. ~2,460,000 today.
- DST
- Daylight Saving Time. Clocks spring forward 1 hour in spring, fall back in autumn. Not observed in some countries and US states.
- Business day
- Monday through Friday excluding public holidays. Definition varies by country (Friday-Saturday weekend in many Middle East states).
- Pomodoro
- Francesco Cirillo's productivity technique. 25-minute focus block + 5-minute break. Long break after 4 cycles.
Frequently asked questions
Short answers to the most common time & date questions.