Guides

How age and dates really work

29 plain-language guides: calculating age by hand, Excel and Google Sheets formulas, leap-year birthdays, school cut-off dates, zodiac and more.

Featured · How age works Leap Year Birthdays: How Age Is Calculated Born on February 29? Learn how age is calculated for leap year birthdays, when you legally age a year, and how calculators handle Feb 29. 14 minute read Read the guide

How age works

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Corrected Age for Premature Babies: How to Calculate It

How Old Am I in Months? Convert Years to Months, Weeks & Days

How old am I in months? Convert your age to total months, weeks, days. Worked example: 36 years 5 months = 437…9 minute read

How to Calculate Age at Death From Date of Birth and Date of Death

Learn how to calculate age at death from date of birth and date of death, including completed years, exact age, leap years,…15 minute read

Excel, Sheets and code

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Excel, Sheets and code

How to Calculate Age in Excel | DATEDIF Formula Guide

Learn to calculate age in Excel with the DATEDIF formula. Step-by-step examples for exact age in years, months, and days from a…12 minute read

Excel, Sheets and code

Age Calculation Formula for Developers: A Calendar-Safe Approach

Learn a calendar-safe age calculation formula for developers, including DOB logic, leap years, month-end dates, timezones, validation, and test cases.22 minute read

Excel, Sheets and code

Age Calculator Formula | Exact Age From Date of Birth

Learn the exact age calculator formula step by step. See how years, months, and days are computed from any date of birth,…13 minute read

School, law and retirement

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School, law and retirement

How to Calculate a Child’s Age on a Cutoff Date

Learn how to calculate a child's exact age on a school cutoff date, step by step, with examples for birthdays before, on,…14 minute read

School, law and retirement

What Age Is Considered Senior Citizen? Benefits, Discounts & Definitions

What age is senior citizen? Learn the 50, 60, 62, 65, and 67 thresholds, typical senior discounts, and how to find when…11 minute read

School, law and retirement

Social Security Full Retirement Age Chart by Birth Year

Find your Social Security full retirement age in the official birth-year chart, from 65 for 1937 births to 67 for 1960 and…8 minute read

Birthdays and zodiac

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Birthdays and zodiac

2026 Year of the Horse: What It Means for Your Chinese Zodiac Sign

2026 is the Year of the Fire Horse, starting February 17. See what it means for your Chinese zodiac sign, all 12…13 minute read

Birthdays and zodiac

How Old Were Famous People at Key Moments? Ages That Surprise You

Famous people ages that surprise: how old were Mozart (8), Einstein (26), Colonel Sanders (62) at key moments? Verify any age with…8 minute read

Birthdays and zodiac

Chinese Zodiac by Birth Year: Find Your Animal Sign

Use the chinese zodiac by year table to find your animal sign, learn the year-mod-12 cycle, Chinese New Year boundaries, elements, and…12 minute read

Family and relationships

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Family and relationships

Is a 10-Year Age Gap Too Much? What Research Says

Is a 10-year age gap too much? We review relationship research, the half-plus-seven rule, and when decade-apart couples thrive.12 minute read

Family and relationships

Parent-Child Age Difference: What’s Typical Around the World?

What's a typical parent-child age difference? Explore global averages, generational labels, and how to calculate your family age gap.9 minute read

Family and relationships

How Many Years Apart Are We? Sibling & Family Age Gaps Explained

Find out exactly how many years apart you and your siblings are, plus typical family age gaps explained.8 minute read