Months Between Two Dates
Updated: May 2026
Months are unequal in length, which makes counting months between dates trickier than counting days or weeks. A 6-month lease, a 24-month loan or a quarterly subscription all require knowing the exact number of complete months and the remaining days — especially when dates fall near the end of a month.
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How partial months are handled
The standard method for counting complete months compares the day-of-month of the end date to the day-of-month of the start date. If end-day ≥ start-day, the month count is simply the difference in calendar months. If end-day is less than start-day, one month is subtracted and the remaining days are the difference to the end of the prior month.
For example, January 15 to March 10 is 1 month and 23 days (not 2 months), because March 10 is before the 15th anchor day. January 15 to March 15 is exactly 2 months. January 31 to February 28 (in a common year) is 28 days — less than one month — because February simply does not have a 31st day.
When a contract says "12 months from signing", the end date is the same calendar date one year later — January 5 to January 5 is exactly 12 months regardless of whether the year is a leap year. Counting 365 days instead would give January 5 in a common year but January 4 in a leap year, which is wrong.
Rental leases and tenancy agreements
Residential and commercial leases are expressed in months. A 12-month lease starting September 1 ends August 31 the following year. A 6-month lease starting on March 15 ends on September 14 (the day before the 6-month anniversary). Knowing the exact end date matters for giving notice, planning moves and calculating rent pro-rations for partial months.
Pro-rated rent for a partial month is the daily rent multiplied by the number of days occupied. The daily rate is calculated as the monthly rent divided by the number of days in that specific month — not a flat 30 or 365÷12 average. February at $1,500/month is $53.57/day; August at the same rate is $48.39/day.
Mortgages and loan terms
Mortgage amortisation is expressed in months. A 30-year mortgage is 360 monthly payments; a 15-year mortgage is 180. The remaining term at any point is the number of months between today and the final scheduled payment date. Knowing this figure helps when evaluating refinancing options, early payoff scenarios or comparing loan offers with different term lengths.
- 15-year mortgage — 180 months, higher monthly payment, less total interest
- 20-year mortgage — 240 months, moderate balance
- 30-year mortgage — 360 months, lower monthly payment, more total interest
For a loan taken out in March 2020 with a 30-year term, the remaining months as of any date in 2026 can be calculated by counting months between today and March 2050.
Subscriptions and service contracts
Annual and multi-year subscriptions are priced and billed monthly. When you cancel mid-cycle or switch plans, the number of months remaining determines your refund or credit eligibility. Many SaaS tools offer annual billing at a discounted rate — knowing exactly how many months remain helps compare the cost of keeping the annual plan versus switching to monthly.
For employment contracts, "6 months' notice" or "3 months' probation" counts calendar months. A probation period starting October 1 ends December 31. Starting October 15 ends January 14. The calculator shows the months-and-days breakdown so you can confirm dates before communicating them.
Frequently asked questions
How do you count months between two dates when they fall on different days?
Compare the day of month. If the end day is greater than or equal to the start day, the month count is the calendar difference. If the end day is smaller, subtract one month and add the remaining days. The Flowfiles calculator handles this automatically and shows the breakdown as X years, Y months, Z days.
What happens when the start date is January 31 and you add one month?
February does not have 31 days, so the result clamps to the last day of February — February 28 in a common year, February 29 in a leap year. This is standard calendar behaviour and reflects how most legal and financial contracts interpret "one month later".
How many months is one year and a half?
18 months exactly (12 + 6). A period from January 1, 2024 to July 1, 2025 is 18 months.
Is 30 days the same as one month?
No. One calendar month can be 28, 29, 30 or 31 days. Saying "30 days from now" and "one month from now" give different dates in months with 28, 29 or 31 days. Use the calculator to get the precise date for each convention.