How this calculator works
Weeks and months do not divide evenly. This page uses an average month of 30.4375 days, one twelfth of a 365.25 day year, so an average month is 2,629,800 s and a week is 604,800 s. Four weeks is 28 days, which is 0.9199 average months, not one month. A calendar month runs 28 to 31 days, so a date calculation that crosses month boundaries can differ from the average by up to a few days.
Formula
average months = weeks x 604800 / 2629800. weeks = average months x 2629800 / 604800. One average month is 4.34821 weeks, and four weeks is 0.919918 average months.
Worked example
4 weeks = 0.919918 average months. 1 week = 0.229979 month. 8 weeks = 1.83984 months. 13 weeks = 2.98975 months. 26 weeks = 5.97947 months. 52 weeks = 11.9589 months, slightly under one year.
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Frequently asked questions
Is 4 weeks the same as 1 month?
No. Four weeks is 28 days, while an average month is 30.4375 days. Four weeks is about 0.92 average months, and a calendar month can be 28, 29, 30 or 31 days.
Why use an average month?
A single fixed month makes arithmetic consistent. For a precise answer over actual dates, count the calendar days between them instead, because leap years and month lengths change the total.
How many weeks are in a year?
A 365.25 day year is 52.1786 weeks, so 52 weeks fall one or two days short of a year. Most calendar years contain 52 weeks plus one or two extra days.
Can I use this to work out a rental end date?
Use the actual start date and the calendar terms in the agreement. Four-week billing periods and calendar-month billing periods have different lengths; the average here only compares durations.