The International Fixed Calendar is a calendar system where every year aligns with the same days of the week and dates, ensuring consistency in weekly patterns. It was first proposed by Moses B. Cotsworth in 1902. This calendar divides the year into 13 equal-sized months, each consisting of 28 days, resulting in a total of 364 days. Leap years are calculated similarly to the Gregorian calendar, with an additional day added every four years. However, in the International Fixed Calendar, the extra day is inserted between June 28 and July 1, known as "Sol," effectively creating a 365-day leap year.

While the month names align with those of the Gregorian calendar, an extra month called "Sol" is inserted between June and July. This arrangement starts each year on a Sunday and ends on a Saturday, ensuring that the first day of each month falls on a Sunday and the last day on a Saturday. This consistency aids in planning and daily routines.

The International Fixed Calendar enhances calendar consistency by ensuring that the same dates align with the same weekdays each year.