12month

12month is a term used to denote a period of twelve consecutive months. In ordinary use it appears as 12-month or twelve-month, while "12month" without a hyphen is uncommon but may appear in product names, identifiers, or informal labels.

In the Gregorian calendar, a 12-month interval typically corresponds to a calendar year, comprising January through December. A common year has 365 days and a leap year 366 days. Months vary in length from 28 to 31 days, and a leap day is added to February every four years, with century years treated according to the 400-year rule.

In business and finance, the 12-month period is a standard horizon for planning, budgeting, and reporting. Rolling 12-month measures track performance over the immediately preceding 12 months, helping smooth seasonality and provide a consistent baseline for comparison. Fiscal years may start in months different from January, while still representing a 12-month window for accounting and analysis.

In analytics and data work, a 12-month moving average or 12-month trailing metric reduces short-term volatility and highlights longer-term trends. Such measures presume regular data frequency and may be adjusted to account for seasonality or irregular reporting.

Culturally, most modern administrative systems use a 12-month year, though some calendars employ lunar or lunisolar months that do not align perfectly with the solar year. The widespread adoption of the Gregorian calendar has standardized the 12-month year in most international contexts.

See also: twelve-month period, annual report, fiscal year, rolling metric.