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Baby weeks to months converter
A baby month is about 4.35 weeks, so 20 weeks is about 4.6 months and a 6 month old is about 26 weeks. Type weeks or months below to convert either way, or find the week in the chart.
20 weeks is about 4.6 months: 4 months and 18 days.
Uses the average month of 30.4 days. For your baby's exact age on the calendar, use the baby milestone calendar tool.
Every week and month, counted for you
Little works out your baby's age, puts the right week or month badge on each milestone photo, and reminds you on the day. Free for iPhone and iPad, no account.
How to convert baby weeks to months
Multiply the weeks by 7 to get days, then divide by 30.4, the average length of a month. For 20 weeks: 20 × 7 = 140 days, and 140 ÷ 30.4 = 4.6 months. Going the other way, multiply months by 4.35 to get weeks.
Dividing by four is the shortcut most people reach for, and it is wrong by about a week every three months. By the first birthday it says 13 months. The converter and chart here use the real average.
This gives an age, not a date. To know the exact day your baby turns a month older, which shifts with 28, 30 and 31 day months, use the baby milestone calendar. The first 12 weeks are also when weekly photos are worth taking; our newborn weekly photo ideas cover what to shoot.
Baby weeks to months chart, week 1 to 52
| Weeks | Months | Exact |
|---|---|---|
| 1 week | 0.2 | 0 mo, 7 d |
| 2 weeks | 0.5 | 0 mo, 14 d |
| 3 weeks | 0.7 | 0 mo, 21 d |
| 4 weeks | 0.9 | 0 mo, 28 d |
| 5 weeks | 1.1 | 1 mo, 5 d |
| 6 weeks | 1.4 | 1 mo, 12 d |
| 7 weeks | 1.6 | 1 mo, 19 d |
| 8 weeks | 1.8 | 1 mo, 26 d |
| 9 weeks | 2.1 | 2 mo, 2 d |
| 10 weeks | 2.3 | 2 mo, 9 d |
| 11 weeks | 2.5 | 2 mo, 16 d |
| 12 weeks | 2.8 | 2 mo, 23 d |
| 13 weeks | 3 | 2 mo, 30 d |
| 14 weeks | 3.2 | 3 mo, 7 d |
| 15 weeks | 3.4 | 3 mo, 14 d |
| 16 weeks | 3.7 | 3 mo, 21 d |
| 17 weeks | 3.9 | 3 mo, 28 d |
| 18 weeks | 4.1 | 4 mo, 4 d |
| 19 weeks | 4.4 | 4 mo, 11 d |
| 20 weeks | 4.6 | 4 mo, 18 d |
| 21 weeks | 4.8 | 4 mo, 25 d |
| 22 weeks | 5.1 | 5 mo, 2 d |
| 23 weeks | 5.3 | 5 mo, 9 d |
| 24 weeks | 5.5 | 5 mo, 16 d |
| 25 weeks | 5.7 | 5 mo, 23 d |
| 26 weeks | 6 | 5 mo, 30 d |
| 27 weeks | 6.2 | 6 mo, 6 d |
| 28 weeks | 6.4 | 6 mo, 13 d |
| 29 weeks | 6.7 | 6 mo, 20 d |
| 30 weeks | 6.9 | 6 mo, 27 d |
| 31 weeks | 7.1 | 7 mo, 4 d |
| 32 weeks | 7.4 | 7 mo, 11 d |
| 33 weeks | 7.6 | 7 mo, 18 d |
| 34 weeks | 7.8 | 7 mo, 25 d |
| 35 weeks | 8 | 8 mo, 2 d |
| 36 weeks | 8.3 | 8 mo, 9 d |
| 37 weeks | 8.5 | 8 mo, 16 d |
| 38 weeks | 8.7 | 8 mo, 23 d |
| 39 weeks | 9 | 8 mo, 30 d |
| 40 weeks | 9.2 | 9 mo, 6 d |
| 41 weeks | 9.4 | 9 mo, 13 d |
| 42 weeks | 9.7 | 9 mo, 20 d |
| 43 weeks | 9.9 | 9 mo, 27 d |
| 44 weeks | 10.1 | 10 mo, 4 d |
| 45 weeks | 10.3 | 10 mo, 11 d |
| 46 weeks | 10.6 | 10 mo, 18 d |
| 47 weeks | 10.8 | 10 mo, 25 d |
| 48 weeks | 11 | 11 mo, 1 d |
| 49 weeks | 11.3 | 11 mo, 8 d |
| 50 weeks | 11.5 | 11 mo, 15 d |
| 51 weeks | 11.7 | 11 mo, 22 d |
| 52 weeks | 12 | 11 mo, 29 d |
Baby weeks and months questions
How many months is 16 weeks for a baby?
About 3.7 months, which is 3 months and 21 days. A 16 week old baby is in their fourth month and turns four months old at about 17 weeks.
How many weeks are in a month for a baby?
About 4.35 weeks. A month averages 30.4 days, so counting four weeks per month drifts by roughly a week every three months. That is why a 12 week old is not quite three months old.
Is 12 weeks the same as 3 months?
Not quite. Twelve weeks is 84 days, about 2.8 months. A baby reaches three months at around 13 weeks.
When should I switch from weeks to months for my baby's age?
Most parents count in weeks for the first 12 weeks, then switch to months. Months take over until about age two, when years and months become easier.
Why do doctors count a baby's age in weeks?
Babies change quickly in the first weeks, and a few days can make a difference to feeding, sleep and growth checks. Weeks are precise; months are easier to say once the pace slows down.