📅 Date & Time

Date & Time Calculator

Free online date and time calculators — find the gap between two dates, add or subtract from a date, look up the weekday, work out an exact age, measure a duration, or count down to a deadline. Every tool shows a worked example and instant results.

✓ Date math

✓ Weekday & ISO week

✓ Age & countdown

✓ 100% Free

Date & time calculators

Pick a calculator below. Each opens a dedicated page with a worked example and instant in-browser output.

Date Calculator

Add or subtract days, weeks, months & years from a date.

Date Difference

Days, weeks & years/months/days between two dates.

Day of the Week

Weekday, day-of-year & ISO week for any date.

Exact age in years, months and days.

Hours & minutes between two times (overnight aware).

Days, weeks & live time until a future date.

Count working days (Mon–Fri) between two dates.

ISO 8601 week number, day of year and weekday.

Add / Subtract Time

Shift a date & time by days, hours and minutes.

Epoch time to a UTC date and back, with milliseconds.

Convert a time between world zones, DST-aware.

Hours worked & pay from clock in/out, overnight shifts.

Time between two clock times in decimal & H:MM, with breaks.

Time (add/subtract)

Add or subtract durations in hours, minutes and seconds.

Convert HH:MM to decimal hours and back for payroll.

Months Between Dates

Full calendar months & years between two dates, end-of-month safe.

Weeks Between Dates

Weeks and leftover days between two dates, plus total days.

Is any year a leap year? Shows the 4/100/400 rule and next leap year.

Day of the Year

Day number 1–366, days remaining, weekday and percent of year elapsed.

Add Days to Date

Add or subtract days from a date; result date and weekday, leap-safe.

Quarter of the Year

Which quarter Q1–Q4, its date range, day into quarter and days remaining.

About these date & time calculators

This is the date and time hub of AI Calculator. It brings together the calendar tools people reach for most — counting the days between two dates, shifting a date forward or back, finding which weekday a date falls on, working out an exact age, timing a duration, or counting down to an event. Each calculator is a standalone page that runs instantly in your browser and walks through a worked example so the method is clear, not just the answer.

The tools pair naturally: use the date calculator to find a deadline from a start date, the date difference calculator to measure the gap the other way, and the day of the week calculator to see which weekday any result lands on. The age and countdown tools cover birthdays and deadlines. All work on whole calendar dates and handle leap years automatically.