# 123AgeCalculator

> Free, exact age calculators: your age in years, months and days, age in days, weeks and seconds, birthday countdown, age difference, dog and cat years and more. No sign-up, nothing stored.

123AgeCalculator (123agecalculator.com) is a free website of age and date calculators. Ages are counted on the calendar — whole years, then whole months, then days — never by dividing a day count by 365 or 30.44, so results match how people and most legal and medical forms count age. Every result has a URL, works without JavaScript, and nothing the user enters is stored. There are no accounts, ads or tracking cookies.

## Your age

- [Age Calculator](https://123agecalculator.com/): Exact age in years, months and days, plus totals and your next birthday.
- [Age in Days Calculator](https://123agecalculator.com/age-in-days-calculator): Days since you were born, and when you turn 10,000 days old.
- [Age in Weeks Calculator](https://123agecalculator.com/age-in-weeks-calculator): Weeks since birth, plus a "life in weeks" grid.
- [Age in Months Calculator](https://123agecalculator.com/age-in-months-calculator): Age in months and days, ideal for babies and toddlers.
- [Age in Seconds Calculator](https://123agecalculator.com/age-in-seconds-calculator): A live counter of your age in seconds, minutes and hours.
- [Birthday Calculator](https://123agecalculator.com/birthday-calculator): Days until your next birthday and the weekday it lands on.
- [Age Difference Calculator](https://123agecalculator.com/age-difference-calculator): The exact age gap between two people, and who is older.
- [Birth Year Calculator](https://123agecalculator.com/birth-year-calculator): Birth year — or exact birth date — from an age.

## Life stages

- [Baby Age Calculator](https://123agecalculator.com/baby-age-calculator): Baby age in weeks and months, with corrected age for preemies.
- [Chronological Age Calculator](https://123agecalculator.com/chronological-age-calculator): Test-date age in years;months;days, with the working shown.
- [Retirement Age Calculator](https://123agecalculator.com/retirement-age-calculator): Social Security full retirement age and key dates from 62 to 70.
- [Generation Calculator](https://123agecalculator.com/generation-calculator): Boomer, Gen X, Millennial, Gen Z or Alpha — by birth year.

## Around the world

- [Korean Age Calculator](https://123agecalculator.com/korean-age-calculator): Traditional Korean age, year age and international age.
- [Chinese Zodiac Calculator](https://123agecalculator.com/chinese-zodiac-calculator): Your animal and element, placed by Lunar New Year.

## Pets & fun

- [Planet Age Calculator](https://123agecalculator.com/planet-age-calculator): Your age in Mercury, Mars, Jupiter and Saturn years.
- [Dog Age Calculator](https://123agecalculator.com/dog-age-calculator): Dog years to human years, by size and by DNA.
- [Cat Age Calculator](https://123agecalculator.com/cat-age-calculator): Cat years to human years, with the life stage.

## Guides

- [How age is calculated](https://123agecalculator.com/how-age-is-calculated): the counting rules, month-end and 29 February conventions, time zones, and the sources behind every table.
- [All calculators](https://123agecalculator.com/calculators): every calculator and which one to use.

## Linking to a result

Every calculator accepts its inputs in the query string, so a link can open a finished result. Dates are YYYY-MM-DD.

- Age Calculator: https://123agecalculator.com/?dob=1990-06-15&as_of=2026-10-30
- Age in Days Calculator: https://123agecalculator.com/age-in-days-calculator?dob=1990-06-15&as_of=2026-10-30
- Age in Weeks Calculator: https://123agecalculator.com/age-in-weeks-calculator?dob=1990-06-15&as_of=2026-10-30
- Age in Months Calculator: https://123agecalculator.com/age-in-months-calculator?dob=2025-03-10&as_of=2026-10-30
- Age in Seconds Calculator: https://123agecalculator.com/age-in-seconds-calculator?dob=1990-06-15&tob=08%3A30
- Birthday Calculator: https://123agecalculator.com/birthday-calculator?dob=1990-06-15&as_of=2026-10-30
- Age Difference Calculator: https://123agecalculator.com/age-difference-calculator?dob1=1988-03-04&dob2=1991-05-09&as_of=2026-10-30
- Birth Year Calculator: https://123agecalculator.com/birth-year-calculator?age=36&passed=unsure&as_of=2026-10-30
- Baby Age Calculator: https://123agecalculator.com/baby-age-calculator?dob=2026-06-01&as_of=2026-10-30&ga_w=32&ga_d=0
- Chronological Age Calculator: https://123agecalculator.com/chronological-age-calculator?dob=2018-06-18&as_of=2026-10-30&method=calendar
- Retirement Age Calculator: https://123agecalculator.com/retirement-age-calculator?dob=1962-09-10&claim=67&as_of=2026-10-30
- Generation Calculator: https://123agecalculator.com/generation-calculator?year=1990
- Korean Age Calculator: https://123agecalculator.com/korean-age-calculator?dob=1990-06-15&as_of=2026-10-30
- Chinese Zodiac Calculator: https://123agecalculator.com/chinese-zodiac-calculator?dob=1990-01-20
- Planet Age Calculator: https://123agecalculator.com/planet-age-calculator?dob=1990-06-15&as_of=2026-10-30
- Dog Age Calculator: https://123agecalculator.com/dog-age-calculator?years=3&months=0&size=medium
- Cat Age Calculator: https://123agecalculator.com/cat-age-calculator?years=3&months=0

If as_of (or another "on this date" field) is left out, the calculator uses today's date.

## Key facts

- Age convention: whole calendar years and months up to the last anniversary of the birth date, then the days since it — 28 February to 31 March is 1 month 3 days.
- When the anniversary day does not exist in a month (30 February, 31 April), it falls on the 1st of the next month: 31 January to 1 March is exactly 1 month, and 29 February birthdays complete each year on 1 March in common years.
- Chinese zodiac: by Lunar New Year (1900–2100 table), not by 1 January.
- Korean age: international age has been the legal standard in South Korea since June 28, 2023.
- US full retirement age: 67 for anyone born in 1960 or later (Social Security Administration).
- Dog years: 16 × ln(age) + 31 (Wang et al., Cell Systems, 2020) alongside the common size-based chart.
- Price: free. Last updated: 2026-10-30