How do I calculate age in months?

To calculate age in months, multiply complete years by 12 and add remaining complete months. For example a child born 2 years and 4 months ago is 28 months old. The age in months formula is: Age in Months = (Years x 12) + Months remaining.

What is the age in months formula?

The age in months formula is: Age in Months = (Complete Years x 12) + Complete Months + (Remaining Days divided by Days in Current Month). Example: 3 years and 5 months = 41 complete months. This monthly age calculator uses this formula automatically.

How do I convert age to months?

To convert age to months multiply years by 12 and add remaining months. 1 year = 12 months. 2 years = 24 months. 3 years = 36 months. 5 years = 60 months. This age to months conversion is done instantly by the calculator above.

What is a baby age calculator used for?

A baby age calculator converts birth date to exact age in months for pediatric use. Pediatricians track infant age in months for vaccine scheduling, growth chart plotting, and developmental milestone assessment up to 24 months.

What is infant age in months used for in medicine?

Infant age in months is used for vaccine scheduling, CDC developmental milestone tracking, growth chart percentiles, medication dosage, and WIC eligibility. CDC publishes milestone checklists at 2, 4, 6, 9, 12, 18, and 24 months.

What is adjusted age for a premature baby?

Adjusted age counts from the original due date rather than actual birth date. A baby born 8 weeks early who is 6 months chronologically has an adjusted age of about 4 months. The AAP recommends using corrected age for developmental assessment until age 2.

At what age do you stop counting in months?

Most pediatricians count age in months until 24 months which is 2 years. After age 2 age is expressed in years. CDC milestone checklists track development monthly up to 24 months then switch to years.

Age in Months Calculator — CalculatorCove

Select Your Purpose

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General Age

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Baby Milestones

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Eligibility Check

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Development Track

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Premature Baby

Date of Birth Enter the date of birth to calculate from

Calculate As Of Defaults to today — or choose any date

Original Due Date (Required for premature) Used to calculate corrected / adjusted age

Current Mode

General age calculation in months, weeks, days & seconds.

Age in Months

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Sources & Methodology

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CDC — Developmental Milestones by Age

Official CDC milestone checklists at 2, 4, 6, 9, 12, 18, and 24 months used for the Pediatric and Development modes

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WHO Child Growth Standards

International standards for infant and child growth used for adjusted age benchmarks in the Premature Baby mode

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American Academy of Pediatrics — Age Terminology

AAP definitions for chronological age, corrected age, and gestational age used in the Premature Baby calculation method

Methodology: Age in months is calculated by counting complete calendar months from date of birth to the reference date, then counting remaining days. Total days are calculated as (reference date - birth date) in milliseconds divided by 86400000. Age in seconds = total days x 86400. For adjusted (corrected) age, the identical formula is applied from the original due date rather than actual birth date, following AAP guidelines. Eligibility thresholds use US federal and state standard age cutoffs. Developmental stage assessments reference CDC milestone checkpoints.

Last reviewed: March 2026 — milestones verified against CDC 2022 updated guidelines and AAP corrected age protocol.

Age in Months Calculator — Complete Guide to Calculating, Converting & Using Monthly Age

Whether you need to calculate age in months for a medical form, track your baby's milestones, or simply answer "how many months old am I?" — this age in months calculator handles all scenarios instantly. Below is everything you need to know about the age in months formula, age to months conversion, and why infant age in months matters in pediatrics.

Age in Months Formula — How This Monthly Age Calculator Works

The age in months formula (also called the monthly age equation) used by this calculator is:

Age in Months = (Complete Years × 12) + Complete Months + (Remaining Days ÷ Days in Month)

Example: Born January 15, 2022 — calculated March 20, 2026
Complete years: 4 → 4 × 12 = 48 months
Complete extra months: 2 (February + March not yet complete) = 2 months
Result: 50 complete months — 1,524 days — 131,673,600 seconds

Note: This monthly age calculator counts complete calendar months only. A child who is 5 months and 29 days old is still clinically 5 months old — they are not yet 6 months until their actual 6-month birth anniversary.

How Many Months Old Am I? — Step by Step

To find out how many months old you are without a calculator:

Here is how to calculate age in months without a calculator:
Step 1: Count the complete years from your birth year to today. Multiply by 12.
Step 2: Count the complete months since your last birthday month.
Step 3: Add them together. That is your age in complete months.
Example: Born October 5, 2020 — today is March 20, 2026. That is 5 complete years (60 months) + 5 months (Nov, Dec, Jan, Feb, March not yet complete = 4 months) = 64 months old.

Or simply enter your birth date in the age in months calculator above — it does all of this in under a second.

How to Convert Age to Months — Quick Reference Table

To convert age to months, multiply years by 12 and add any extra months. Use this age to months conversion table for instant reference — the quickest age conversion to months reference on the web:

Age in Years	Age in Months	Age in Days	Age in Seconds (approx)
3 months	3 months	~91 days	~7.9M seconds
6 months	6 months	~183 days	~15.8M seconds
1 year	12 months	365 days	~31.5M seconds
1.5 years	18 months	548 days	~47.3M seconds
2 years	24 months	730 days	~63.1M seconds
3 years	36 months	1,095 days	~94.6M seconds
4 years	48 months	1,461 days	~126.2M seconds
5 years	60 months	1,825 days	~157.7M seconds
10 years	120 months	3,652 days	~315.6M seconds
18 years	216 months	6,574 days	~567.9M seconds

Baby Age Calculator — Why Infant Age in Months Matters

Wondering how many months old is my baby? This baby age calculator is used by parents, pediatricians, nurses, and childcare providers because infant development happens so rapidly that years are not a precise enough unit in the first two years. A 6-month-old and a 12-month-old are at vastly different developmental stages despite being less than a year apart.

The CDC, WHO, and American Academy of Pediatrics all use infant age in months as the standard unit for:

Vaccine scheduling — vaccines are given at 2 months, 4 months, 6 months, 12 months, 15 months, and 18 months. A single month difference changes which vaccines are due.
Growth chart percentiles — weight-for-age and height-for-age charts use monthly intervals under 24 months.
Developmental milestones — the CDC publishes checklists at 2, 4, 6, 9, 12, 18, and 24 months.
Formula and food introduction — solid foods at 6 months, whole milk at 12 months, honey after 12 months are all monthly-based guidelines.

Monthly Age Calculator for Medical and School Use

Beyond pediatrics, age in months is used in several adult and institutional contexts. School enrollment typically requires children to reach a certain age by a specific cutoff date — most US states require a child to be 5 years old (60 months) by September 1. WIC benefits are available to children under 5 years (60 months). Head Start programs serve children from 3 years (36 months) to 5 years (60 months). This age calculator in months instantly shows whether a child meets any of these thresholds.

Infant Age in Months — Vaccine and Milestone Schedule

Infant Age	Key Vaccines Due	CDC Milestones	Age in Seconds
2 months	DTaP, Hib, IPV, PCV, RV	Smiles, tracks faces, coos	~5.3M
4 months	DTaP, Hib, IPV, PCV, RV	Laughs, holds head, reaches	~10.5M
6 months	DTaP, Hib, PCV, RV, flu	Sits with support, babbles	~15.8M
12 months	MMR, Varicella, Hep A, PCV	First words, pulls to stand	~31.5M
18 months	DTaP, Hep A, flu annual	Walks, 10+ words, points	~47.3M
24 months	Annual flu only	Runs, 2-word phrases	~63.1M

Vaccine schedules shown are the CDC standard schedule. Always confirm with your pediatrician as individual schedules may vary. Source: CDC Immunization Schedule.

💡 Pro tip for parents using this age calculators for babies: When your pediatrician asks your child's age, always give it in complete months for children under 2. Say "18 months" not "1 and a half" — this ensures they are using the correct milestone checklist and vaccine schedule for your child's exact monthly age.

Frequently Asked Questions

To calculate age in months, multiply the number of complete years by 12 and add remaining complete months. For example: a person born on January 10, 2022 is, on March 20, 2026, 4 years and 2 months old = (4 × 12) + 2 = 50 months. For partial months, count the remaining days. This monthly age calculator does all of this automatically from any birth date.

The age in months formula is: Age (months) = (Complete Years × 12) + Complete Months + (Remaining Days ÷ Days in Current Month). For complete months only, drop the days fraction. Example: 3 years, 5 months, and 10 days = 36 + 5 = 41 complete months. This is the same formula used by this age calculator in months.

To convert age to months, multiply years by 12 and add any extra months. Age to months conversion: 1 year = 12 months • 1.5 years = 18 months • 2 years = 24 months • 3 years = 36 months • 4 years = 48 months • 5 years = 60 months. For fractions like 2.5 years, multiply 2.5 × 12 = 30 months. Use the age conversion table in this guide for a complete reference.

To find how many months old you are, enter your date of birth in the age in months calculator above and click Calculate. The calculator counts every complete calendar month from your birth date to today. For example if you were born on June 15, 1990, today March 20, 2026 you are 429 months old (35 years and 9 months × 12 = 429).

A baby age calculator converts birth date to exact age in months for pediatric use. Pediatricians use infant age in months for: vaccine scheduling (vaccines are due at 2, 4, 6, 12, and 18 months), growth chart percentile tracking, CDC developmental milestone assessment, medication dosing, and eligibility for programs like WIC (under 60 months). Most doctors count age in months until 24 months, then switch to years. This months old calculator covers all ages from newborn to adult.

Adjusted age (corrected age) counts from the original due date rather than actual birth date. To calculate: subtract weeks born early from chronological age. A baby born 10 weeks early who is 6 months old chronologically has an adjusted age of approximately 3.5 months. The AAP recommends using corrected age for all developmental assessment until age 2 years, and until age 3 for babies born before 28 weeks gestation. Select the Premature Baby mode in this calculator to see both ages side by side.

Most pediatricians stop counting age in months at 24 months (2 years). After age 2, age is typically expressed in years and half-years (e.g. "2.5 years"). CDC milestone checklists track development monthly up to 24 months, then at 30 months and 4-5 years. However, for premature babies, corrected age in months may be used until age 2-3 depending on how early the baby was born.

To calculate your age in seconds, multiply your age in days by 86,400 (the number of seconds in one day). Examples: a 1-year-old = 365 × 86,400 = 31,536,000 seconds. A 30-year-old ≈ 946,728,000 seconds. A newborn at 30 days = 2,592,000 seconds. This age in months calculator shows your exact second count automatically in the results.

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