Month Difference Calculator
Calculate the exact number of months between two dates, with adjustments for partial months and day-of-month differences.
The number of months between two dates depends on what "a month" means. The calendar months (March 15 to April 15 = 1 month) and 30-day months (March 15 to April 14 ≈ 1 month) give slightly different answers. The date difference calculator on this site reports both.
Example: March 15, 2024 to August 20, 2025
- Full calendar months: 17 months and 5 days
- 30-day months: 523 days ÷ 30.44 ≈ 17.18 months
- Average year fraction: 1.43 years
Two Common Counting Methods
Calendar-month method. Count whole months by going day-of-month to day-of-month. March 15 to April 15 = 1 month. March 15 to April 14 = 0 months and 30 days. This matches how leases, contracts and rent calculations work.
Days-divided-by-30.44 method. An average year has 365.25 days and 12 months, so 365.25 / 12 = 30.4375 days per month. Divide the total day count by this for a decimal month answer. Used in financial calculations where consistent monthly periods matter more than calendar alignment.
Common Use Cases
- Pregnancy weeks-to-months (40 weeks ≈ 9.2 months)
- Loan term remaining in months
- Lease length verification
- Visa duration and immigration calculations
- Tenure tracking for benefits eligibility
Use the Full Calculator
The Date Difference Calculator handles every scenario described on this page. For the deeper math and worked examples, read the companion guide.