The monthsInYear accessor property of Temporal.PlainDate instances returns a positive integer representing the number of months in the year of this date. It is calendar-dependent.

For the ISO 8601 calendar, this is always 12, but in other calendar systems it may differ. For example, in calendars using leap months, leap years will have one more month than common years.

The set accessor of monthsInYear is undefined. You cannot change this property directly.

Examples

Using monthsInYear

const date = Temporal.PlainDate.from("2021-07-01");
console.log(date.monthsInYear); // 12

const date2 = Temporal.PlainDate.from("2021-07-01[u-ca=chinese]");
console.log(date2.monthsInYear); // 12

const date3 = Temporal.PlainDate.from("2023-07-01[u-ca=chinese]");
console.log(date3.monthsInYear); // 13; 2023 is a Chinese leap year

Changing to the second last month of the year

You can use monthsInYear to change to the second last month of the year:

const date = Temporal.PlainDate.from("2021-07-01");
const secondLastMonth = date.with({ month: date.monthsInYear - 1 });
console.log(secondLastMonth.toString()); // 2021-11-01

Specifications

Browser compatibility

See also

• Temporal.PlainDate
• Temporal.PlainDate.prototype.with()
• Temporal.PlainDate.prototype.add()
• Temporal.PlainDate.prototype.subtract()
• Temporal.PlainDate.prototype.year
• Temporal.PlainDate.prototype.month
• Temporal.PlainDate.prototype.monthCode
• Temporal.PlainDate.prototype.daysInMonth