AgeCalc Help Documentation

A complete guide to the age calculator, from the first date of birth to the family calendar file.

Last Updated: November 3, 2026

1. Getting Started

1.1 What you need

• A modern browser (Chrome, Edge, Firefox, Safari or Opera) with JavaScript enabled, on a computer, tablet or phone
• Site data allowed for zerodataupload.com, so your settings and saved birthdays are kept between visits
• A date of birth, or any two dates you want to compare

1.2 The layout

The tool is one page with four tabs in the toolbar: Age, Date tools, Birthdays and Settings. To the left of the tabs, the status pill shows the age in force and the birthdays saved, for example "Age 36 years, 2 months" and "Next birthday in 285 days · 4 birthdays saved". How it counts opens a short window with the counting rules and the keyboard shortcuts. On a tablet or phone the cards stack and the tabs fill one row.

1.3 First steps

1. Check the date order in Settings (day-month-year, month-day-year or year-month-day). It starts from your browser's language.
2. On the Age tab, type your date of birth. The age appears as soon as the year is complete.
3. Scroll through the cards below it, or open Date tools for anything else to do with dates.

2. Typing a Date

Every date in the tool uses the same three boxes, for the day, the month and the year, in the order chosen in Settings.

• Typing: the cursor moves to the next box when a box is full, or after a single digit that cannot start a longer number (4 in the day, 2 in the month). A slash, dash, dot, comma or space also moves on.
• Pasting: paste a whole date into any box: 15/08/1990, 15-08-1990, 15 Aug 1990, August 15 1990, 15th August 1990 and 1990-08-15 are all read. A two-digit year is taken as the most recent such year.
• Arrow keys: Up and Down in a box step the day, the month or the year by one, carrying over month and year ends.
• Calendar button: opens your browser's own date picker.
• Check line: the line under the boxes spells the date out with its weekday, or says what is wrong ("April has 30 days"). Years from 1 to 9999 are accepted.

3. The Age Tab

3.1 Date of birth, birth time and Age on

Date of birth is the only field you need. Add birth time opens a time field: with a time, hours, minutes and seconds count from that moment rather than from midnight; the cross removes it. Age on is today unless you change it; set it to any date, past or future, to see the age on that day, and press Today to return to the live count.

3.2 The figure

The Exact Age card shows the years large, then the months and days, a line with the date and the age as a decimal, and three buttons: Copy (the result as a sentence), Copy link (an address that opens the same result; it contains the date of birth) and Save to Birthdays (opens the Birthdays window with the date filled in). On a birthday a line says so.

3.3 The totals

Six tiles give the age in months, weeks, days, hours, minutes and seconds. Months and weeks show the days left over. With the live count, hours, minutes and seconds go up every second; with another Age on date they are counted to the start of that day.

4. Year Rings

The Year Rings card draws one ring for every full year lived, like the rings of a tree trunk, with a darker ring every ten years and the decades labelled. The amber arc is the current year, and its length shows the share of the way to the next birthday. The caption under the rings gives the count and the share.

• Mouse: point at a ring to see the dates of that year; click to keep it selected, click again to let go.
• Touch: tap a ring.
• Keyboard: focus the rings with Tab, then use the arrow keys to step through the years, Home and End for the first and the current year, Esc to clear.

5. Next Birthday, Born On and Milestones

• Next Birthday: a live countdown in days, hours, minutes and seconds, the date and the age turned, the half birthday when it is still ahead, a note for 29 February birthdays, and Add to calendar every year.
• Born On: the day of the week, the day of the year, the ISO week, the star sign and the Chinese zodiac (each opens the Zodiac signs tool), the birthstone and birth flower of the month, the generation and whether it was a leap year.
• Milestones: the next four round numbers ahead and the last two passed, with All milestones for the full table and a calendar button on each one ahead.
• Birthdays by Day of the Week: every birthday so far counted by the weekday it fell on, as bars; the bar of the next birthday's weekday is amber. Every birthday opens the table.
• More With This Date of Birth: buttons that open the date tools with your date of birth already filled in.

6. Date Maths Tools

Open Date tools and pick a tool from the list on the left (on a phone, the list comes first and All tools brings it back). Each tool remembers its inputs.

• Date difference: two dates, Swap, and Count the end date too. The result gives years, months and days, total days, weeks, months, working days, weekend days, hours, minutes, seconds and years as a decimal. Choose the weekend (Saturday and Sunday, Sunday only, Saturday only, Friday and Saturday, Friday only, or none) and list days off to skip, one per line or separated by commas.
• Add or subtract: a start date and an optional time, Add or Subtract, and any number of years, months, weeks, days and hours. Tick Count the days as working days to skip weekends and days off. The steps are listed, and a note explains when a day such as 31 April does not exist.
• Days from today: a number of days, weeks, months or years ago or from now, with quick picks from 7 to 10,000 days.
• Day of the week: the weekday of any date with the month around it, the day of the year, the week number, the quarter, the next years the date falls on the same weekday and the next years with the same calendar.

7. Age Tools

• Age on a date: the age on any date for any date of birth, with quick picks such as 1 January next year and in 10 years.
• Reaching an age: the date of turning any age in years and months, a table of common ages from 16 to 100, and the option to show the retirement date under the Indian central government rule.
• Age limit check: the date of birth, the cut-off date, the minimum and maximum age, the extra years allowed (quick picks 3, 5, 10 and 15) and what the maximum means: under that age, or up to the end of that age. The verdict, the age on the cut-off date and the allowed dates of birth follow.
• Age gap: two names and dates of birth; who is older and by how much, the age of the older one when the younger was born, the day one was twice as old as the other, the combined age today and the day it reaches 100.

8. Fun With Age

• Age on other planets: the age in the years of each planet from Mercury to Neptune, the next birthday there, and the days lived on Mars (sols).
• Dog and cat years: a pet's age in human years from its age or birth date, or a human age in pet years. Dogs by adult size; the full chart opens below the result.
• Life in numbers: days, Saturdays, leap days and Friday the 13ths lived and trips around the Sun (exact), and full moons, heartbeats, breaths, blinks, hours asleep, meals and steps (estimates; heartbeats, breaths and blinks count up live).
• Zodiac signs: the Chinese zodiac animal, element and lunar year, checked against the date of Chinese New Year from 1900 to 2040, the twelve animals with yours marked, and the star sign with its dates, birthstone and flower. With a year only, the sign is worked out from the year.

9. Life and the World

• Life expectancy: the average life expectancy at birth for women, men or both in 48 countries or the world, the share of it lived, the average years left, and Life in weeks: one square for each week, one row for each year. Point at a square to see its dates.
• World clock: the time now in your list of cities, or at a chosen time in the city you compare from (type a time or drag the slider in 15-minute steps; Now returns to the live clock). Add cities or time zones by name, up to 30; the bin removes one.

10. Birthdays

1. Press Add a birthday, type the name, the day and the month, the year if you know it, and an optional note, then Save birthday.
2. The list sorts itself by whose birthday comes next, in four groups: today, the next 30 days, the next three months and later. Each row says the weekday, how many days are left and the age turned.
3. The buttons on a row show the full age on the Age tab, edit the entry or delete it; a deletion can be undone from the notice for a few seconds.
4. Add all to calendar saves one calendar file with every birthday, repeating each year.

11. Settings

• Date order: day-month-year, month-day-year or year-month-day, for typing and for showing dates.
• Weeks start on: Monday or Sunday, for the month calendars and the weekday bars.
• Birthdays on 29 February: 28 February or 1 March in other years.
• Large numbers: 1,234,567 or the Indian 12,34,567, with millions and billions or lakhs and crores in the milestones.
• Remember my date of birth: when off, the date is forgotten when you close the page.

The light and dark theme is the site's own switch at the top right and is shared with every page.

12. Backup and Delete

• Save a backup file writes one file with the date of birth, the saved birthdays, the tool inputs and the settings.
• Restore from a backup reads such a file and asks whether to add its birthdays to the list (entries with the same name and date are skipped) or to replace everything.
• Delete everything removes all that AgeCalc keeps in this browser after you confirm. Nothing else of the site is touched.

13. Keyboard Shortcuts

• /: type a date of birth (outside a text field)
• Alt+1 to Alt+4: switch between Age, Date tools, Birthdays and Settings
• Left and Right on the tabs: move between them
• Up and Down in a date box: step the day, month or year by one
• Arrow keys, Home and End on the rings: step through the years
• Esc: close a window

14. What Is Remembered

The browser's storage on this device holds, under the tool's own name, the date of birth and birth time (unless Remember is off), the saved birthdays, the inputs of every tool, the list of world clock cities, the last tool opened and the settings. The Age on date is not kept: each visit starts with today. The light or dark theme is shared with the rest of the site.

15. Troubleshooting

• The date was read the wrong way round. Read the line under the boxes, then change Date order in Settings.
• Nothing appears after typing the date. The year needs all four digits; the line under the boxes says so. A date after the Age on date shows "Not born yet".
• The age is one day off from another calculator. That calculator probably divides days by 365.25 or counts 30-day months; AgeCalc counts calendar months (see the FAQ).
• A calendar file opens as text. Open it with your calendar app, or use its import command, rather than a text editor.
• Nothing is remembered. A notice says when the browser blocks storage (some private windows do). Use a normal window, or keep a backup file.

16. Support

For questions the FAQ does not answer, use the contact form and say which browser and device you use.