These calculators figure out age in ways that go well beyond a simple birthday count. The Age Calculator gives an exact breakdown in years, months, and days, while the Age in Days Calculator drills down further. The Korean Age Calculator and Lunar Age Calculator apply East Asian counting traditions, and a set of pet converters — Cat, Hamster, Bird, and Guinea Pig — translate animal lifespans into human-year equivalents for extra perspective.
Browse the most-popular list to see which calculators people reach for most, or open the Trending tab for what's getting attention right now. All tools are free, need no account, and work on any device.
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Dog Age in Human Years CalculatorConvert your dog's age into human years using the science-based logarithmic formula (16·ln(age)+31), with a linear puppy approximation under 1 year.
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How Old Was I When... CalculatorFind out exactly how old you were when a past event happened. Enter your birth date and the event date to get your age in years, months and days.
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School Starting Age CalculatorFind out how old a child will be on the school cutoff date and whether they meet the minimum starting age. Enter birth date, cutoff date, and required age.
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Age on a Specific Date CalculatorFind out exactly how old someone was (or will be) on any chosen date. Enter a birth date and target date to get age in years, months and days.
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When Will I Turn 21 Calculator (US)Find the exact date you turn 21 and reach the legal US drinking age. Enter your birthday to see the date and days remaining until you can legally drink.
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Dog Age in Dog Years by Breed Size CalculatorConvert your dog's age to human years by breed size. Small, medium, and large dogs age differently — get a more accurate dog-years estimate instantly.
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Age of Majority Date CalculatorFind the exact date you reach the age of majority. Enter a birthdate and choose 18 or 21 years to see the calendar date and days remaining.
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Zodiac Sign Compatibility Calculator by BirthdateEnter two birthdates to find your sun signs and an element-based zodiac compatibility score out of 100. Free, instant astrology match calculator.
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Birthstone CalculatorFind your birthstone by birth month. Instantly see your modern and traditional gemstone plus its meaning for any month from January to December.
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Age from Birth Year CalculatorFind out how old you are if you only know your birth year. Year-only age estimate: current year minus birth year, with the birthday-not-yet-reached range.
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Days Lived CalculatorFind out exactly how many days you have lived. Enter your date of birth and an end date to count the total days, weeks, hours and years between them.
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Milestone Birthday Date CalculatorFind the exact date and weekday of any milestone birthday — 16th, 18th, 21st, 30th, 40th, 50th and more — from a date of birth.
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Relationship Length CalculatorFind out exactly how long you've been together. Enter your relationship start date to get years, months, days, total weeks and total days.
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Age Difference Between Two People CalculatorFind the exact age gap between two people in years, months and days. Enter both birthdays to get the precise difference and total days apart.
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Baby Age in Weeks and Months CalculatorFind your baby's age in weeks, days and whole months from their date of birth. Quick, accurate infant age calculator for any "as of" date.
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Social Security Full Retirement Age CalculatorUS Social Security tool: enter your birth year to find your full retirement age (FRA) when you qualify for 100% unreduced retirement benefits.
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Retirement Age CalculatorFind the exact date you reach your chosen retirement age and a live countdown in days and years from your birth date.
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How Old Will I Be On a Future Date?Find out exactly how old you'll be on any future date. Enter your birthday and a target date to get your age in years, months and days.
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Birthday Day of Week CalculatorFind what day of the week you were born and the weekday of your next birthday. Free day-of-week calculator using Zeller's congruence for any date.
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Half Your Age Plus Seven Dating Rule CalculatorApply the popular "half your age plus seven" dating rule. Enter your age to find the youngest and oldest partner age considered socially acceptable.
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Average Age CalculatorCalculate the average (mean) age of a group instantly. Enter each person's age, separated by commas, to get the mean, total, youngest and oldest.
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How Many Days Old Am I?Find out exactly how many days, weeks, and hours old you are. Enter your birthdate and a reference date to calculate your age in days.
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Horse Age CalculatorConvert your horse's age into human years instantly. Uses the standard 12/7/2.5 horse-to-human age formula for a quick, accurate estimate.
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Kitten Age CalculatorEstimate a kitten's age in weeks and months from its weight. Uses the vet rule of thumb of about 1 pound per month for the first 6 months.
Frequently asked questions
What is the difference between standard age, Korean age, and lunar age?
Standard age counts completed years since your birth date. Korean age traditionally adds one year at birth and increases again each New Year's Day, so you may be one or two years older in Korean reckoning than in international age. Lunar age follows the traditional Chinese lunar calendar and can produce a different figure again depending on the time of year.
How accurate are the age calculations?
The standard Age Calculator and Age in Days Calculator are exact, based on calendar arithmetic from your birth date to today's date. Korean and lunar age results follow their respective traditional systems faithfully. For any legal, official, or administrative purpose, verify your age against an authoritative source such as your birth certificate or official records.
How do the pet age converters work?
Each converter uses species-specific lifespan models — for example, a commonly referenced equivalency scale for cats, or research-based charts for hamsters and birds — to translate an animal's age into a comparable human-year figure. They are designed as an informative and fun guide rather than a precise biological measurement.
Do you store my date of birth or any personal information?
No. Calculations run entirely in your browser. Your date of birth and any other inputs are never sent to our servers or saved after you leave or refresh the page.
Which age calculators are most popular?
The list is ordered by real visitor usage. The main Age Calculator and Korean Age Calculator typically rank at the top. Open the Trending tab to see which tools are climbing fastest right now, or Recently Added for the latest arrivals.
