Baby Age Calculator
Find a baby's age in weeks, months, and days from the birth date, for milestones and appointments.
👶 What is the Baby Age Calculator?
The baby age calculator works out how old an infant is in the units parents and health professionals actually use: weeks and days for the early months, and months and days after that. Enter the date of birth and a date to check, and it returns the age in weeks, in months, and as total weeks and days.
New parents reach for it all the time. Baby age is quoted in weeks at first, so knowing that your baby is "8 weeks and 6 days" helps you follow feeding guides, sleep expectations, and developmental milestones that are all pegged to weeks. Vaccine and check-up schedules are set in weeks and months, so a quick, exact age avoids confusion at appointments. Grandparents and carers use it to answer the constant "how old is the baby now" question with a precise number.
The reason a dedicated tool helps is that weeks and months do not line up neatly. Eight weeks is 56 days, but two calendar months is usually 59 to 62 days, so converting by dividing days by 30 drifts off over time. This calculator counts real calendar months from the birth date and separately counts whole weeks, so both figures match how doctors and milestone charts describe age. For babies born prematurely, milestones often use corrected age counted from the due date; this tool gives the actual age, which you can then adjust by the weeks of prematurity.
It is useful because it turns a birth date into every common way of stating a baby's age at once, and lets you pick a future date to see how old the baby will be at an upcoming appointment or birthday, with the working shown.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 - Two-month-old
Example 2 - Newborn, a few weeks old
Example 3 - Approaching nine months
❓ Frequently Asked Questions
🔗 Related Calculators
How do you calculate a baby's age in weeks?
Count the total days since birth and divide by 7. The whole number is the weeks and the remainder is the extra days. A baby born on 1 May, on 2 July, is 62 days old, which is 8 weeks and 6 days. This calculator works it out from the two dates.
How many weeks is my baby?
It is the number of full 7-day periods since birth. Enter the date of birth and today's date (or any date) and this calculator shows the age in weeks and days, plus total weeks. For the first two to three months, weeks are the usual way to describe a baby's age.
When do you switch from weeks to months for a baby's age?
There is no strict rule, but weeks are common until about 8 to 12 weeks, after which months become more usual. Many health records and milestone charts use weeks early on and months from around 3 months to 2 years. This calculator shows both so you can use whichever fits.
How do you calculate a baby's age in months?
Count the whole calendar months from the birth date to the current date, then the leftover days. A baby born on 1 May, on 2 July, is 2 months and 1 day old. Calendar months vary in length, so this is more accurate than dividing days by 30.
What is corrected age for a premature baby?
Corrected age is the age counted from the original due date instead of the actual birth date, used to judge development for babies born early. If a baby was born 6 weeks premature, subtract 6 weeks from the actual age. This calculator gives actual age; adjust it by the prematurity for corrected age.
How many months is 8 weeks?
About 2 months, though not exactly, because months are longer than 4 weeks. Eight weeks is 56 days, while 2 calendar months is usually 59 to 62 days. That is why this calculator shows weeks and months separately rather than converting one into the other.
Why not just divide days by 30 for months?
Because calendar months are 28 to 31 days, dividing by 30 drifts off over time. This calculator counts real calendar months from the birth date, so the months and leftover days match how doctors and milestone charts actually describe a baby's age.
Can I find how old my baby will be on a future date?
Yes. Set the second date to a future appointment, birthday, or holiday, and the calculator shows the baby's age in weeks and months on that day. This is handy for planning vaccines, check-ups, or a first-birthday countdown.
Does the baby age calculator handle the day of birth?
It measures the time elapsed since birth, so on the day of birth the age is zero days. From the next day it counts up. This matches how age is normally described, where a newborn is days old before reaching their first week.