Time & Dates

Date arithmetic is full of traps: months of different lengths, leap years, daylight saving changes and time zones that move their offsets twice a year.

These tools count calendar days in UTC to avoid the classic one-day-off errors, and the timers run entirely in your browser tab.

11 tools · updated October 19, 2026

Date Difference Calculator Count the time between two dates as a calendar span in years, months and days and as total days, weeks and hours. Add/Subtract Days Add or subtract a number of days from a date to get the resulting date, its weekday and its ISO week number. Age Calculator Calculate exact age in years, months and days from a date of birth, plus days and weeks lived and the countdown to the next birthday. Time Zone Converter Convert a date and time between two cities using IANA time zone rules, including daylight saving time on the chosen date. Working Days Calculator Count the Monday-to-Friday working days between two dates, inclusive, minus any holidays you list. Retirement Countdown Count down to your planned retirement date in years, months and days, with progress so far and your US Social Security full retirement age. Project Timeline Calculator Find the finish date for a job that needs a given number of working days, skipping weekends and the days off you list. Lunar Calendar Calculator Show the Moon’s phase, illuminated percentage and age for any date, with the dates of the next full and new moons. Shift Schedule Calculator Lay out a rotating shift pattern such as 4 on 4 off or Panama 2-2-3 on an eight-week calendar, with the average weekly hours. Stopwatch Time anything to the hundredth of a second and record laps, with each lap time, the running total and the fastest, slowest and average lap. Pomodoro Timer Run Pomodoro work sessions and breaks automatically, with a long break after every fourth session and adjustable lengths.

Counting days, hours and time zones correctly

Days between two dates, or a date some days away?

If you know both dates, the date difference calculator gives the gap in days, weeks and months. If you know a start date and a number of days, the add or subtract days tool gives the end date. Watch whether a count includes both ends: Monday to Friday is four days apart, but five days if you count both of them, as hotel bookings and leave requests often do differently.

Calendar days or working days?

Deadlines in contracts and shipping are often stated in business days. The working days calculator counts weekdays between two dates and skips any holidays you list, and the project timeline calculator goes the other way, from a start date and a number of working days to a finish date. Public holidays differ by country and employer, so enter the ones that apply to you.

Why are time zone offsets wrong half the year?

Many regions move their clocks for daylight saving time, and not on the same dates: the United States changes on the second Sunday in March and the first Sunday in November, the European Union on the last Sundays of March and October, and much of the world not at all. A fixed table of offsets is therefore wrong for part of the year. The time zone converter looks up each zone for the date you pick.

Ages and countdowns

The age calculator handles leap-year birthdays and gives the exact age in years, months and days, while the retirement countdown works out the date and the time left from a birth date and a retirement age. The moon phase calculator finds the phase on any date.

Timers and rotas

The stopwatch records laps, the Pomodoro timer alternates 25-minute focus blocks with short breaks, and the shift schedule calculator lays a rotating pattern such as four on, four off onto a calendar. All three run in your browser tab, so keep the tab open while they are timing.