Convert Days to Months

There isn’t one. Calendar months are 28, 29, 30, or 31 days. Any conversion to “X months” has to pick a convention. The Gregorian-average 30.436875 is the most defensible for multi-year estimates; 30 is the simplest; calendar-from is the only way to be exact for a specific date range.

Because 365.2425 (the average Gregorian year) ÷ 12 = 30.436875 exactly. The rounded 30.44 is 0.003125 higher per month – over 10 years that accumulates to ~0.375 extra days of drift. The unrounded value is “free precision” at no cost to readability.

Because over a year, 12 × 30 = 360 days – short of 365.25 by 5.25 days. So “30 days” is slightly less than an average month. The default output shows 0.985626 months for 30 days, which is honest. Switch to the “30 d/mo (simplest)” mode if you need the folk convention where 30 days = 1 month exactly.

It walks real month lengths. Start at 2024-01-15, add 91 days: 17 days remain in January, then February has 29 days (2024 is leap), then March has 31. That’s 17 + 29 + 31 + (91 − 17 − 29 − 31) = 17 + 29 + 31 + 14 = 91 days, landing on 2024-04-15. That’s exactly 3 months. No divisor needed.

In the fixed-divisor modes, the Gregorian-average divisor (30.436875) already accounts for leap years on average over 400 years. In calendar-from mode, the leap day is respected literally – starting in February 2024 gives a different answer than February 2023 because 2024 has a 29th.

A date-difference tool subtracts one date from another and reports whole months plus remainder days. This tool takes a day count and asks “how many months is that?” – it doesn’t look at your calendar unless you pick calendar-from mode. For subscription billing or age calculation, date difference is usually what you want.

Because billing engines usually define a “month” as “same day-of-month next month” – so Jan 15 to Feb 15 is 1 month regardless of the 31-vs-28-day asymmetry. This tool’s fixed-divisor modes don’t know about day-of-month semantics. Use calendar-from mode with your start date, or the billing system’s own definition.

Yes. Negative days produce negative months and the split shows the direction. In calendar-from mode, negative days walk backwards through earlier months, respecting their actual lengths.

Multiply months by the divisor you chose: 3 × 30.436875 = 91.31 days (Gregorian avg). In calendar-from mode the reverse is “add N months to a start date”, which our dedicated months-to-days converter handles.

Yes. Everything computes in your browser with plain arithmetic. No upload, no tracking, no account. Load the page once and it keeps working offline indefinitely.