To count weeks between two dates, find the total days and divide by seven; the remainder is the partial week. Counting months needs a different approach because calendar months are unequal. Compare the day of the month and count complete month boundaries rather than treating every month as 30 days.
Weeks are fixed; months are not
Four weeks always contain 28 days. A month can contain 28 to 31. That is why 12 weeks and three months can end on different dates even when they sound similar.
Count completed units
From 4 January to 18 January is two complete weeks. From 4 January to 3 February is not yet one complete calendar month; 4 February completes it. For a plain-language result, report “three months and five days” instead of forcing the remainder into a decimal.
Match the unit to the question
Use days for exact deadlines, weeks for short plans, and calendar months for anniversaries, subscriptions or age. The difference calculator can show several units, but your purpose decides which is clearest.
Keep the original dates
Store both source dates beside the duration. If a future reader sees only “six months,” they cannot check the calculation or understand whether it used full months or an estimate.
Questions people ask
Is four weeks the same as one month?
No. Four weeks is 28 days, while most calendar months are longer.
How should I show a partial week?
Use complete weeks plus remaining days, such as two weeks and three days.
