What next?
One duration, several units. These are the other ways to read it.
How to use this converter
- Type a number in years, months or weeks.
- The other two boxes update automatically.
- Read the plain-terms breakdown and the day count alongside.
What your result means
Years and months convert exactly (1 year = 12 months), but weeks don’t divide evenly into either, so week figures are averages. The tool converts everything through days — a year of 365.25 days (to include leap years), a month of that year ÷ 12, and a week of 7 days — so the three units stay consistent with each other.
Why this one is different
The answer leads in plain English — two years, four months and three weeks — because that sentence is usually the thing being written down, with the exact single-unit conversions listed under it. Where a span crosses months of unequal length, the day figure is marked approximate instead of implying a precision it has not got.
A month isn’t a whole number of weeks
Weeks (7 days) don’t divide neatly into months or years, which is why pregnancies are tracked in weeks but ages in years. An average month is about 4.35 weeks and a year about 52.18 weeks — the tool uses these averages so your three values always agree.
Formula
1 month ≈ 4.35 weeks · 1 week = 7 days
Example conversion
Converting 18 months:
18 × 4.35 ≈ 78 weeks
Quick reference
Where the four-weeks-a-month shortcut costs real money
Four weeks feels like a month and is not. Twelve lots of four weeks is 48 weeks, and a year has 52 and a bit, so the shortcut quietly loses a month of every annual total. On a weekly rent of £200 that is a £800 discrepancy over a year — which is exactly why letting agents convert weekly rents by multiplying by 52 and dividing by 12, giving £866.67 a month rather than £800.
The same arithmetic runs through payroll. Someone paid weekly receives 52 payments a year; someone paid every four weeks receives 13; someone paid monthly receives 12. Three different rhythms for the same annual salary, which is why a four-weekly payslip is smaller than a monthly one and why one month a year appears to contain two paydays.
For anything longer than a couple of months, work in the unit the obligation is actually written in and convert once. Converting back and forth — weeks to months to years and back — accumulates the 4-versus-4.35 error at every step, and it is always in the direction that understates the total.
Frequently asked questions
How many weeks are in a month?＋
About 4.35 weeks on average (30.44 days ÷ 7). A calendar month isn’t a whole number of weeks.
How many weeks are in a year?＋
About 52.18 weeks (365.25 days ÷ 7), which is why a year is often said to be 52 weeks plus a day or two.
Why is a month not exactly four weeks?＋
Four weeks is 28 days, and only February in a common year is that short. The real average is about 4.35 weeks, so twelve months is 52 weeks rather than 48.
How many working weeks are in a year?＋
Around 46 to 47 for a typical UK employee once 28 days of statutory leave and bank holidays are taken out of 52.
How do I convert a weekly rate to a monthly one?＋
Multiply the weekly figure by 52 and divide by 12, which is the same as multiplying by 4.333. Multiplying by 4 understates the annual total by a month's worth.
Why do some years have 53 weeks?＋
A 365-day year is 52 weeks and one day, so week-numbered calendars occasionally need a 53rd week to stay aligned. It happens roughly every five or six years under ISO 8601.
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Assumptions & limitations
Why three units that seem simple do not divide neatly:
- A year is not a whole number of weeks (52.18) and a month is not a whole number of weeks (4.35), so conversions between them are always approximate.
- Pregnancy, tenancy and finance terms each use their own convention — 40 weeks, calendar months and 12 monthly payments respectively — and they do not agree with each other.
- For an exact answer between two real dates, use the date difference calculator rather than a unit conversion.