Month Calculator

Subtract the start year from the end year, multiply by 12, then add the difference in months. If the end day is earlier than the start day, subtract one month and count the leftover days. This calculator handles all of that automatically. See also our calculate Days Remaining, Years & Months — Countdown Timer.

By default, the calculation counts up to but not including the end date. Checking 'include end date' adds one extra day to the total, which is useful when you want to count both the first and last day of a period (e.g., a contract that runs from Jan 1 to Jan 31 inclusive).

A leap year has 366 days instead of 365, adding February 29. Leap years occur every 4 years (with exceptions for century years not divisible by 400). This calculator accounts for leap years when computing total days between dates.

Leap years occur in years divisible by 4 — such as 2024, 2028, 2032. Century years (e.g. 1900) are not leap years unless also divisible by 400, like the year 2000. You might also find our calculate Unix Timestamp (seconds), UTC Date & Time & ISO 8601 — Epoch Converter useful.

A monthsary is a monthly anniversary — a celebration marking each month that has passed since a significant date, such as the start of a relationship. This calculator can tell you how many months have elapsed since any date.

February is the shortest month, with 28 days in a standard year and 29 days in a leap year. All other months have either 30 or 31 days.

90 days is approximately 2 months and 29–30 days, or roughly 2.96 months, since the average month is about 30.44 days. The exact count depends on which specific months are involved.

This calculator uses the Gregorian calendar, which is the internationally accepted civil calendar today. It replaced the Julian calendar and accounts for leap years to keep the calendar aligned with Earth's orbit around the sun.