New parents quickly learn that baby age isn’t counted like adult age. For the first stretch of life it’s measured in weeks, then months, and only later in years. Knowing how to convert between them helps at check-ups, with feeding and sleep guidance, and when people ask “how old is the little one?”
Why weeks first, then months
In the early days, so much changes so fast that weeks are the meaningful unit — health visits, growth checks and developmental notes are often framed weekly. Around the two-to-three month mark, weeks become unwieldy and most people switch to months. By the first birthday, age in years takes over.
A quick reference
| Age | Roughly equals |
|---|---|
| 4 weeks | about 1 month |
| 8 weeks | about 2 months |
| 13 weeks | about 3 months |
| 26 weeks | about 6 months |
| 52 weeks | 1 year |
Working out the exact age
To get your baby’s precise age, count from their date of birth to today. The age in days calculator gives the exact number of days and weeks lived, while the age calculator shows months and days. Both count real calendar days, so you don’t have to juggle the “4.3 weeks per month” conversion yourself.
Corrected age for premature babies
If a baby was born early, health professionals often use a corrected (adjusted) age — the age the baby would be if born on the due date — when tracking development. To find it, work out the age from the actual birth date, then subtract the number of weeks the baby was early. Your pediatric team will guide you on when corrected age matters and when to stop using it.
This is general information, not medical advice. Always follow your healthcare provider’s guidance for your child.