Months to days converter

What This Tool Does

This converter translates a number of months into the matching number of days — and in both directions at once. The two input fields are coupled live: typing into one updates the other without a button press. An optional disclosure block shows the matching hours, minutes and seconds for finer-grained planning.

Pure-client. Every value stays inside your browser. No server, no tracking, no cookie wall. The tool works offline as soon as the page has loaded once.

Why Three Month-Length Modes?

“One month” is not a single value. February has 28 or 29 days, April and September have 30, January and March have 31. “Six months of trial period” measures a different number of days than the “six monthly instalments” a bank calculates. Three definitions are in practical use, and the converter makes all three visible.

Julian mean (30.4375 days) — default

The Julian year is 365.25 days; divided by twelve months it gives exactly 30.4375 days. This number delivers the astronomically correct average across a four-year cycle that includes one leap day. For everyday questions — trial period, pregnancy, contract term — it is the best default.

Gregorian mean (30.436875 days) — secular exact

The Gregorian calendar year averages 365.2425 days across 400 years because the century-year exception drops three leap days per 400 years (1700, 1800, 1900 are not leap years, 2000 is). Divided by twelve months that yields 30.436875 days per month — marginally below the Julian mean. Over ten years the gap totals about 0.075 days, or roughly two hours.

30-day model (30 days) — banking and contract standard

Banks, insurers and lease contracts usually use a flat 30 days per month — the 30/360 day-count convention. Twelve months equal 360 days, not 365. The missing day per month (5.25 per year) is not a rounding error but a deliberate convention: equal-length months simplify daily interest accrual considerably. Corporate bonds, German-standard mortgages and many lease contracts use this convention.

Which Use Cases Does the Tool Surface?

The use-case table groups the most common search intents into a single overview — from trial periods through pregnancy to passport validity.

Work and contracts

The German statutory maximum trial period under §622(3) BGB is six months (182.625 Julian days). A classical apprenticeship under BBiG runs 36 months (1,095.75 days). The §573c BGB rental notice period is three months (91.3125 days), six months for landlords after five years of tenancy. Anyone planning a notice-letter receipt date should reach for the Julian mean.

Family and health

A pregnancy in clinical convention runs 40 weeks postmenstrual — exactly 280 days from the first day of the last menstrual period. The naive nine-month estimate delivers 273.94 Julian days, about six days under the medical standard. German statutory sick pay under §48 SGB V runs a maximum of 18 months (547.875 days) for the same illness. Child-benefit extension during conscription under §32 EStG covers twelve months (365.25 days).

Travel and identity

German passports for people under 24 are valid for six years (72 months, 2,191.5 days). Adult passports run ten years — 3,652.5 days. Travellers to the United States, China or Turkey should keep at least six months (182.625 days) of remaining validity — many embassies refuse a visa otherwise.

Banking and interest

A ten-year fixed-rate mortgage period covers 120 months. In Julian averaging that is 3,652.5 days, in the 30-day model 3,600 days — a 52.5-day gap. This is why banks must always disclose the day-count method behind rate offers. Anyone comparing effective rates should check whether “month” means Julian or 30/360 for the lender.

Which Mental Rule of Thumb Works Without a Tool?

Multiply months by 30 and add a healthy eighth of the month count — that is the Julian approximation in your head. Six months trial = 6 × 30 + 0.4 × 6 ≈ 182 days. For most everyday questions it is enough. For exact deadline math, pension calculations or precise sick-pay duration, the converter takes over with two- to four-decimal rounding per field.

The mental rule has a limit: over long horizons the model gap shows. For 240 months (a twenty-year mortgage) the Julian mean yields 7,305 days, the 30-day model 7,200 — a 105-day gap. Across short terms (three or six months) the difference stays below two days.

Why Use a Coupled Live Converter Instead of a Table?

A static table only covers discrete values. Six months is listed — seven months may not be. As soon as a question mentions an odd number (trial extension by two weeks, mortgage remainder 27.5 months), mental math starts. The coupled live converter handles any value instantly, in both directions, with no submit click. The use-case table underneath supplies the context (contract basis, statutory anchor, medical convention) that a bare number cannot.

Pure-client also means values never leave your device. No server logs, no cookies, no cookie wall. The input even tolerates either decimal style (German comma, English period).

What Other Time Tools Are Related?

More tools from the kittokit ecosystem that fit the topic:

• Years to Days — years to days with three year-length modes and life-expectancy anchors.
• Age Calculator — exact age in years, months and days with leap-year-safe math.
• Date Calculator — difference between two dates, plus date-plus-X-days.
• Working Days Calculator — workdays between two dates, German holidays included.