To convert weeks to months, divide the number of weeks by 4.345, the average number of weeks in a month. So 12 weeks is about 2.8 months, 16 weeks is about 3.7 months, 20 weeks is about 4.6 months, and 26 weeks is almost exactly 6 months. The table below covers every common number of weeks.
Weeks to months conversion table
| Weeks | Days | Months (approx.) | In plain terms |
|---|---|---|---|
| 1 | 7 | 0.23 | about a quarter of a month |
| 2 | 14 | 0.46 | about half a month |
| 4 | 28 | 0.92 | just under 1 month |
| 6 | 42 | 1.38 | 1 month and ~1.5 weeks |
| 8 | 56 | 1.84 | just under 2 months |
| 10 | 70 | 2.30 | 2 months and ~1 week |
| 12 | 84 | 2.76 | 2 months and ~3.5 weeks |
| 13 | 91 | 2.99 | 3 months (one quarter) |
| 14 | 98 | 3.22 | 3 months and ~1 week |
| 16 | 112 | 3.68 | 3 months and ~3 weeks |
| 18 | 126 | 4.14 | 4 months and ~4 days |
| 20 | 140 | 4.60 | 4 months and ~2.5 weeks |
| 24 | 168 | 5.52 | 5½ months |
| 26 | 182 | 5.98 | 6 months (half a year) |
| 30 | 210 | 6.90 | just under 7 months |
| 36 | 252 | 8.28 | 8 months and ~1 week |
| 40 | 280 | 9.20 | 9 months and ~1 week |
| 52 | 364 | 11.96 | 1 year (minus 1 day) |
The formula, and why 4 doesn't work
A month isn't 4 weeks. The average month is 30.44 days long (365.2425 ÷ 12), which is 4.345 weeks. So:
- Months = weeks ÷ 4.345
- Weeks = months × 4.345
If you divide by 4 instead, you overestimate: 26 weeks ÷ 4 = 6.5 "months", when it's really about 6. The error grows the longer the period.
Calendar months vs average months
The table uses average months. When you count from an actual date, the answer depends on which months you cross, because they range from 28 to 31 days. For example:
- 12 weeks from January 5, 2027 is March 30, 2027, which is 2 months and 25 days, because February is short.
- 12 weeks from July 5, 2027 is September 27, 2027, which is 2 months and 22 days.
To get the exact date, use a calculator: 12 weeks from today, 16 weeks from today, 20 weeks from today or 26 weeks from today. Each page also has a box for counting from any start date.
Pregnancy: weeks, months and trimesters
Pregnancy is one of the most common reasons people convert weeks to months, and it's counted in a specific way. Doctors count a pregnancy from the first day of the last menstrual period, about two weeks before conception, and a full-term due date is 40 weeks from that day. That's about 9.2 average months, which is why "nine months" is a slight underestimate.
Trimesters are commonly described as:
| Trimester | Weeks (commonly used) | Approx. months |
|---|---|---|
| First | Weeks 1–13 | Months 1–3 |
| Second | Weeks 14–27 | Months 4–6 |
| Third | Week 28 to birth | Months 7–9 |
Different sources draw the lines slightly differently, and your due date may be adjusted after an ultrasound, so always use the dates your doctor or midwife gives you. This table is for general information, not medical advice.
Other everyday conversions
- Training plans: a 16-week marathon plan is about 3.7 months, so starting in early July puts race day in late October.
- Probation periods: "90 days" is about 12.9 weeks, or just under 3 months. See days to months.
- Project timelines: a 6-week sprint cycle fits about 8.7 times into a year.
- Visa and lease terms: these are usually written in months or days, not weeks, so convert carefully, and check our guide to counting deadlines.
Need an exact answer? Enter any two dates in the date duration calculator to see the time between them in weeks, months and days, or count forward with 6 months from today.
Frequently asked questions
How many months is 12 weeks?
About 2.76 months, or 2 months and roughly 3½ weeks.
How many months is 20 weeks?
About 4.6 months, or 4 months and roughly 2½ weeks.
Is 26 weeks 6 months?
Very nearly. 26 weeks is 182 days; six calendar months is 181–184 days.
How many weeks are in 3 months?
About 13 weeks (13.04 on average).