What this calculator does
Weeks to months has no single exact answer, because a month is not a fixed number of weeks; it ranges from just over 4 weeks in February to close to 4.5 weeks in a 31-day month. This calculator uses an average month length, 4.348214 weeks, so a conversion like 26 weeks in months gives a consistent, usable figure rather than depending on which specific months are involved.
It works in both directions: enter a number of weeks to see the equivalent in months, or a number of months to see the equivalent in weeks. Pregnancy milestones and age-in-weeks questions are the most common reason people ask for a weeks-to-months conversion, and the default figure below is set to 26 weeks for exactly that reason.
The formula
Weeks are converted to months by dividing by 4.348214, and months to weeks by multiplying by the same figure. That factor comes from an average calendar month of 30.4375 days (365.25 days in a year, divided by 12 months), converted to weeks by dividing by 7.
| Term | Meaning |
|---|---|
| Week | A fixed unit of exactly 7 days. |
| Average month | A month length averaged across the calendar year, 30.4375 days, used because actual months vary from 28 to 31 days. |
| 4.348214 | The number of weeks in an average month: 30.4375 days ÷ 7 days per week. |
The inputs explained
| Field | What to enter |
|---|---|
| Value | The value to convert. Defaults to 26, a common pregnancy and age-in-weeks milestone. |
| Convert | Choose whether to convert weeks to months, or months to weeks. |
When to use it
Converting 26 weeks in months
A common milestone, such as a pregnancy stage or a baby's age, given in weeks converts to just under 6 months using the average month figure, which is the usual way these milestones are described in months.
Comparing an age or duration quoted both ways
When one source states an age or duration in weeks and another in months, converting both to the same unit checks whether they actually agree.
Converting a project or notice period from months to weeks
A notice period or project length quoted in months converts to weeks when it needs lining up against a schedule that runs week by week.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Weeks to months, at common milestone values
A range of week values, each converted to months.
| Weeks | Months | In days |
|---|---|---|
| 14 | 3.220 | 98.0 days |
| 16 | 3.680 | 112.0 days |
| 18 | 4.140 | 126.0 days |
| 20 | 4.600 | 140.0 days |
| 26 | 5.979 | 182.0 days |
| 40 | 9.199 | 280.0 days |
Months to weeks, at common values
A range of month values, each converted to weeks.
| Months | Weeks | In days |
|---|---|---|
| 1 | 4.348 | 30.4 days |
| 3 | 13.045 | 91.3 days |
| 6 | 26.089 | 182.6 days |
| 9 | 39.134 | 273.9 days |
| 12 | 52.179 | 365.2 days |
| 18 | 78.268 | 547.9 days |
Questions
How many months is 26 weeks?
About 5.98 months, using an average month of 4.348214 weeks. In everyday terms this is usually rounded to roughly 6 months.
How many months is 18 weeks?
About 4.14 months, using the same average-month conversion.
Why is there no exact answer for weeks to months?
A month is not a fixed length: it ranges from 28 days in February to 31 days in months like January or July. This calculator uses an average month, 30.4375 days, so the conversion is consistent regardless of which specific months are involved.
How many weeks is 9 months?
About 39.1 weeks, using the average-month factor, which is why a full-term, 40-week pregnancy is usually described as "about 9 months" rather than exactly 9.
For the number of days a specific number of weeks from today, see the add or subtract from a date calculator. For the full time unit ladder including months and years, see the time converter.