52 weeks ≠ 12 months
A calendar year has about 52.18 weeks, so “12 months” and “52 weeks” don’t line up perfectly—handy to remember for milestone charts.
Counting quirks
Age in Weeks & Months (Baby-Friendly)
Dates
Result: Enter dates and click Calculate.
How we count weeks & months
Weeks: Whole weeks + remaining days (e.g., 12 weeks, 3 days) and a decimal view (e.g., 12.43 weeks).
Months:
- Calendar months — whole months + days (e.g., 3 months, 5 days).
- Decimal months — total days ÷ average month length ≈ 30.44.
Leap years and real month lengths are respected. Feb 29 birthdays follow calendar arithmetic naturally.
About the Age in Weeks and Months Calculator
If you have ever wondered "how many weeks old am I?" or "how many months old is my baby?", this calculator gives a clear, calendar-accurate answer in seconds. It converts a birth date and a target date into an easy-to-read breakdown in weeks and months, so you can understand age beyond just years. The result is presented in friendly formats such as whole weeks plus remaining days and calendar months plus remaining days, with optional decimal views for quick comparisons.
The idea is simple: count the real days between two dates, then express that span in different units. Weeks are based on seven-day blocks, so you will see both total weeks and leftover days. Months are a bit trickier because month lengths vary. This tool shows calendar months by counting full months on the calendar and then the remaining days, and it also provides a decimal months estimate by dividing total days by the average month length of about 30.44 days. Leap years and real month lengths are respected, which keeps the results accurate for dates like February 29.
Using the calculator is straightforward. Enter a date of birth, then choose a second date such as today or a future date. Click Calculate to see the age expressed in weeks and months. If you need to start over, hit Clear. You can use the results for a current age, or set a future date to see how old someone will be at an upcoming milestone, appointment, or event.
Real-world uses include baby and toddler milestone tracking, pregnancy or newborn development charts, school enrollment timing, medical paperwork that asks for age in weeks or months, and planning celebrations like 100 weeks old or 18 months old. It is also helpful for pet ages, fitness progress tracking, or any situation where "months old" matters more than just years. Because everything runs locally in your browser, your dates stay private and the calculations update instantly.
FAQs
Which month should I use?
For baby milestones, many parents prefer calendar months. Decimal months are handy for charts or spreadsheets.
Can I choose a future date?
Yes—set any target date to see age at that time (e.g., first day of school).
Is my data private?
Yes. Everything runs in your browser; no dates are uploaded.
5 Fun Facts about Weeks & Months of Age
1,000-week milestone
Hitting 1,000 weeks old lands around 19 years and 3 months—a fun, under-celebrated birthday.
Hidden milestone
Leap days add up
Each leap day adds ~0.033 months. Over a decade that’s roughly 10 extra days—enough to nudge “months old” totals.
Leap lag
Baby growth by the week
Many babies double birth weight near 4–5 months (≈20 weeks) and triple it by ~12 months—why weekly check-ins matter early on.
Milestone math
“40 weeks” isn’t exact
Full-term pregnancies range from 37 to 42 weeks; those extra weeks shift newborn ages by nearly a whole month on early charts.
Early variance