Baby Age Calculator

Pop in your little one's birth date and instantly see their age in weeks, months, and days — with an adjusted age for babies born early.

📖 How it works & FAQ

Date of birth

Age as of

Weeks born early (if premature)

How your baby's age adds up

In the first year, age is usually counted in weeks, then months, then years. This calculator takes a birth date and a reference date and works out the exact gap in three ways at once: full weeks (with leftover days), full calendar months (with leftover days), and the raw total number of days. That way you can answer "how many weeks old is she?" at a pediatric visit and "how many months?" for a milestone chart without doing the math in your head.

What "adjusted age" means for premature babies

A baby born early hasn't had as long to develop, so doctors often track an adjusted (or corrected) age. The rule is simple: subtract the number of weeks your baby arrived early from their actual age. A 20-week-old born 6 weeks early has an adjusted age of 14 weeks. Corrected age is typically used for developmental milestones until roughly age 2, then most babies "catch up." Enter the weeks early and this tool shows both ages side by side.

How to use it

Enter your baby's date of birth.
Leave Age as of set to today, or pick a past or future date to check a specific milestone.
If your baby was premature, type how many weeks early they were born.
Read the result cards — weeks, months, days, and adjusted age update instantly.

These figures are estimates for general reference, not medical advice — always check with your pediatrician about your baby's growth and development.

FAQ

When do I stop counting in weeks?: Many parents and doctors switch from weeks to months around 3 months (about 12 weeks), and to years after the first birthday. This tool shows all three so you can use whichever fits.
How is "months old" calculated?: By calendar months, not by dividing days by 30. A baby born on the 15th turns "one month" on the 15th of the next month, with any extra days shown separately.
How long should I use adjusted age?: Pediatricians generally use corrected age for premature babies until about 2 years old, then chronological age. Ask your doctor about your child specifically.
Can I check a future date?: Yes — set "Age as of" to any date to see how old your baby will be at a birthday, holiday, or upcoming appointment.