Weeks to Months Calculator
Enter any number of weeks to see how many months, days, and years that equals. The calculator uses the standard Julian-average month (365.25 / 12 = 30.4375 days) to give the most accurate general-purpose conversion. Switch to reverse mode to convert months back to weeks, or read the reference table for common values from 1 week to 104 weeks.
How to convert weeks to months
To convert weeks to months, divide the number of weeks by 4.348214. This factor comes from the Julian calendar average: 365.25 days per year divided by 12 months gives 30.4375 days per month, and dividing that by 7 days per week gives 4.348214 weeks per month. The reciprocal, about 0.230137, is the number of months in a single week. So 13 weeks is 13 x 0.230137, which equals about 2.99 months, essentially 3 calendar months.
Why the conversion is not a simple divide-by-4
A common shortcut is to divide weeks by 4, but that implies a month of exactly 28 days, which only applies to February in a non-leap year. In reality the Gregorian year averages 365.2425 days, so each month averages 30.437 days and each month contains 4.348 weeks, not exactly 4. Using 4 as the divisor understates the month count by about 8.6 percent over a full year. For everyday estimates the difference is small, but for project timelines, payroll periods, or medical contexts it compounds quickly. This calculator uses the Julian-average factor (365.25 / 12 / 7) for maximum general-purpose accuracy.
Weeks and months in pregnancy
Obstetric dating counts pregnancy in completed weeks from the first day of the last menstrual period (LMP). The first trimester ends at the close of week 13 (about 2.99 months), the second trimester runs from weeks 14 to 27 (months 3 to roughly 6.2), and the third trimester spans weeks 28 to 40 (months 6.4 to 9.2). A full-term pregnancy is defined as 39 to 40 weeks, equivalent to about 8.97 to 9.20 months. Because clinical care is managed in weeks and the first prenatal visit is scheduled by week count, always use the week number in medical contexts rather than rounding to months.
Months to weeks: the reverse conversion
To go in the other direction, multiply months by 4.348214. For example, 6 months equals 6 x 4.348214 = 26.09 weeks, or about 182.6 days. This is useful when a contract, subscription, or study period is described in months but you need to schedule it by week. Switch the Direction selector above to "Months to weeks" and the calculator applies the reciprocal factor automatically.
Weeks to months reference chart
| Weeks | Months | Days | Milestone |
|---|---|---|---|
| 1 | 0.23 | 7 | |
| 2 | 0.46 | 14 | |
| 4 | 0.92 | 28 | |
| 6 | 1.38 | 42 | |
| 8 | 1.84 | 56 | 2 months approx. |
| 10 | 2.30 | 70 | |
| 12 | 2.76 | 84 | |
| 13 | 2.99 | 91 | End of 1st trimester |
| 16 | 3.68 | 112 | |
| 20 | 4.60 | 140 | |
| 24 | 5.52 | 168 | |
| 26 | 5.99 | 182 | 6 months approx. |
| 27 | 6.21 | 189 | End of 2nd trimester |
| 39 | 8.97 | 273 | Full-term pregnancy |
| 40 | 9.20 | 280 | Standard 40-week term |
| 52 | 11.96 | 364 | One year |
| 78 | 17.93 | 546 | 1.5 years |
| 104 | 23.91 | 728 | 2 years |
Calculated using the Julian-average month of 30.4375 days. Values are rounded to 2 decimal places.
Frequently asked questions
How many months is 13 weeks?
13 weeks is approximately 2.99 months, essentially 3 calendar months. Exactly: 13 x (12 / (365.25 / 7)) = 2.991 months, or 91 days. This is the most-asked version of the question because week 13 marks the end of the first trimester in pregnancy.
Is 4 weeks exactly 1 month?
No. Four weeks is 28 days, but an average month is 30.4375 days (365.25 / 12). So 4 weeks equals about 0.92 months, not 1.0. A true calendar month is 4.348 weeks on average. The only months that contain exactly 28 days are February in non-leap years.
How many weeks is 3 months?
3 months is approximately 13.04 weeks (3 x 4.348214 = 13.04). In days that is 91.3 days. Depending on which specific months are involved, the span could range from 89 to 92 days on a real calendar.
How many weeks is 6 months?
6 months is approximately 26.09 weeks, or about 182.6 days. In a calendar sense, the exact number depends on which 6 months you are counting - a span that includes February and two 30-day months will be shorter than one with all 31-day months.
What is the most accurate conversion factor for weeks to months?
The most accurate general-purpose factor is 0.230137 months per week, derived from 12 / (365.25 / 7). This uses the Julian year of 365.25 days, which is the standard for everyday time conversions. The Gregorian year (365.2425 days) gives a marginally different factor (0.230148) that is negligible for any practical use.
How do I convert weeks to months and days?
Multiply the weeks by 0.230137 to get total months. Take the integer part as the whole months. Multiply the decimal remainder by 4.348214 to get the leftover weeks, then multiply that by 7 to get leftover days. This calculator shows the whole-months and remaining-weeks breakdown in the result panel.
How many weeks is 9 months?
9 months is approximately 39.13 weeks (9 x 4.348214). This is why a full-term pregnancy is quoted as "about 40 weeks" - the extra fractional week in the 9-month average rounds to 40 weeks when measured from the last menstrual period.