Countdown Timer and Age Calculator

What this page works out, and why mental math gets it wrong

Pick a date and this page shows how much of it is left in days, hours, minutes and seconds, redrawn every second. Pick a birth date instead and the second panel gives an exact age in years, months and days, plus the total number of days lived. Both answers are calculated on your own device from your own clock.

Counting the days in your head is where it goes wrong. Months are 28 to 31 days long, February gains a day in leap years, and "about six weeks" quietly turns into five or seven once you cross a month boundary. Subtracting two dates in a spreadsheet gives a whole number that was accurate at the moment you typed it and slowly stops being true afterward. A countdown reads the clock every second instead, so it never goes stale.

What it is good for

Exams and dissertation deadlines, a launch or an on-sale time, a wedding, a flight, a visa expiry, a contract end date, New Year's Eve on a screen at a party, a classroom timer, and the count-up cases: days sober, days into a training plan, days since a pet came home.

Two panels, and which one answers your question

The page holds two independent calculations that do not affect each other. Which one you fill in depends on whether the date in your hand is in the future or in the past.

• Countdown, at the top: you have a future date and want to know how much time is left.
• Birth date and age, at the bottom: you have a past date and want to know how much has accumulated since.
• The target time field: leave it empty and the page counts whole days, the same way the due date calculator does. Fill in the real clock time when the moment matters, such as a gate closing, a departure, an exam room opening or a sale going live, and the display splits into days, hours, minutes and seconds.
• The event name field: it changes the label above the digits, the title of the downloaded calendar event and the share link. It does not change any number.
• A past date in the target field: the display flips to counting up by itself, so use the same panel for days since something happened.

How to set up a deadline countdown and get it into a calendar

1. Put the date in Target date. Add the clock time in Target time if the hour matters, for example 09:00 for an exam start. Leave it empty to see whole days only.
2. Type something into Event name, such as "Finals" or "Launch". It appears above the digits and becomes the title of the calendar event in the next step.
3. The digits update on their own, with no button to press. The line underneath restates the same interval as one total: total days, total hours and total seconds.
4. Press Download .ics to turn the target into a calendar event. Import it and your calendar will remind you 15 minutes before it starts, which is the part a web page cannot do for you.
5. To leave it on a screen, press Fullscreen. The digits fill the display on a black background, which suits a classroom, a party or a reception screen. Press Esc or the close button in the corner to come back.

How to get an exact age and a total day count

1. Scroll to Birth date and age and put the birth date in the field. It will not accept a date in the future.
2. The result is broken down into completed years, then the leftover months and days. The first number is the age a form asks for, because a birthday that has not happened yet this year is not counted.
3. The days lived line underneath is the one to use for day milestones so far.
4. To find out when a round number such as the 10,000th day falls, put 10000 in Which date is day N? at the bottom. Leave the start empty to count from the birth date, or enter a first date or a quit date instead. The answer is the day the count reaches 10,000, with the start as day 0, the same way the days lived line counts. Anniversary apps usually call the start day 1, which lands one day earlier, so the result spells out that date as well.
5. For a full breakdown, including the countdown to the next birthday and how leap day birthdays are handled, use the age calculator.

Getting the result somewhere useful

• Download .ics: exports the target as a standard iCalendar file that Google Calendar, Apple Calendar and Outlook can all import, so the reminder lives somewhere that will actually interrupt you.
• Copy share link: the address carries the event name and the dates, so whoever opens it sees the same countdown without setting anything up.
• Fullscreen: for a New Year's Eve screen, a classroom clock, a stream overlay or a reception display.

The calendar file is plain: one event 30 minutes long, one reminder 15 minutes before it starts, and times written in UTC so the calendar app converts them back into whatever zone the device is in. Both the length and the reminder can be edited after the import like any other event.

The share link only carries the fields you filled in. Anything left empty is not written into the address, which is why the link is often shorter than you expect.

Time zones, daylight saving and per-device differences

Everything is calculated in your device time zone. The date and time you type are read as local wall clock time, so the countdown answers "how long until that moment where I am". When the event happens somewhere else, convert it first with the time zone converter and enter the converted local time. New Year is the case that catches people out, because Auckland and Los Angeles are the better part of a day apart.

Daylight saving can move a countdown by an hour when the interval crosses a clock change, since the number of hours between two local timestamps is not always a multiple of 24. Start and end dates are set by each country and are changed from time to time, and a good part of the world does not observe it at all, so treat the hour figure as approximate across a transition. The day count is not affected.

• Fullscreen: some mobile browsers do not allow an ordinary page element to go fullscreen, and the button will report that it could not. Use a laptop or tablet, or turn the phone to landscape instead.
• The .ics file: on iPhone and iPad, opening the downloaded file usually asks which calendar to add it to. On a desktop you generally save it first and then use the calendar app's import command.
• Background tabs: browsers throttle timers in tabs you are not looking at to save battery, so the seconds may jump when you switch back. The figure is recomputed from the clock rather than accumulated, so it catches up correctly.

Limits worth knowing

• It trusts your device clock: the countdown is only as accurate as the time on the machine showing it. If you need the seconds to be right, such as for a New Year countdown, check that automatic time setting is switched on first.
• It will not remind you: there is no account, nothing runs in the background and there are no notifications. If forgetting is the real risk, download the .ics file and let a calendar do the reminding.
• A share link is public text: the event name and the dates are written into the address, so anything you would not want a stranger to read does not belong in the event name.
• Calendar days only: notice periods, shipping estimates and contract terms are often counted in working days, which excludes weekends and public holidays. A calendar day count will flatter the time you have. The date calculator counts the weekdays between two dates.
• Not an official schedule: this page does arithmetic on the date you type in. Exam dates, filing deadlines, on-sale times and visa expiry dates should be confirmed against whoever publishes them.