Free Date & Time Calculators
Dates are harder than they look: months have different lengths, leap years add a day, and “how many working days” depends on weekends. These calculators handle all of that with exact calendar arithmetic, so you can work out someone’s age to the day, the number of days between two dates, the date a deadline falls on or how long until a birthday. Everything runs in your browser using the same calendar rules every time.
Age and durations
How old, how long and how many days.
Age CalculatorWork out exact age in years, months and days, plus the days until your next birthday.
Days Between Dates CalculatorFind the exact number of days, weeks and business days between any two dates.
Time Duration CalculatorFind the hours and minutes between two times of day, including overnight shifts.
Birthday Countdown CalculatorSee exactly how many days until the next birthday, and what age it turns.
Countdown TimerAn online countdown timer for any duration or a date and time, with a sound alarm and a live clock in the tab title.
Time Zone ConverterConvert a date and time between 40 major time zones, with daylight saving handled for the exact date.Planning with dates
Add or subtract time, count working days and find weekdays or week numbers.
Date Calculator (Add or Subtract Days)Add or subtract days, weeks, months and years from any date.
Business Days CalculatorCount working days between two dates, or add working days to a date, excluding weekends and holidays.
Day of the Week CalculatorFind what day of the week any date falls on, past or future.
Week Number CalculatorFind the ISO week number for any date, and see exactly which week it is.Related reading
Working across countries? See Time zones and daylight saving: a practical guide for remote teams, with the 2026 clock-change dates and overlap charts.
Why calendar maths needs a calculator
A month is not a fixed number of days, so “one month after 31 January” has no obvious answer. These tools use a consistent rule — month-end clamping, so 31 January plus one month is 28 (or 29) February — and show the working. Leap years follow the Gregorian rule: divisible by 4, except century years that are not divisible by 400.
Business-day counts exclude Saturdays and Sundays; if your country or employer observes other holidays, subtract them from the total yourself.
Guides for this topic
How to Calculate Age in Years, Months and Days5 min readHow to Calculate Days Between Dates6 min readHow to Convert Time Zones5 min readFrequently asked questions
How is age calculated?
Count complete years since the birth date, then the remaining complete months and days, borrowing the correct number of days from the previous month when needed.
Are the calculations affected by time zones?
No. Dates are treated as calendar dates, not moments in time, so the answer is the same wherever you are.
Do business-day results include public holidays?
No — only weekends are excluded. Public holidays differ by country and year, so subtract them from the total.
Reviewed September 26, 2026 by the SolveCalcPro editorial team. See our editorial policy. All tools →