How Many Months Between Two Dates
Whether you are calculating your age in months, determining how long a contract runs, or tracking weeks of pregnancy in monthly terms, knowing the number of months between two dates is an essential piece of date math. The challenge is that months are not uniform—they range from 28 to 31 days—so counting them requires a clear method. This guide explains both the calendar-month approach and the average-month approach, walks through real examples, and links to tools that do the work for you. Try our weeks & months between dates calculator or the main date calculator for instant results.
- Two methods: Calendar-month counting (exact) and average-month dividing (approximate, using 30.44 days/month).
- 30.44 days is the average month length derived from the Gregorian calendar cycle (365.2425 ÷ 12).
- Calendar months count month boundaries (e.g., March 15 to June 15 = 3 months), regardless of how many days each month has.
- Month counting is used in age calculation, lease terms, loan amortization, and medical timelines.
- Our calculator handles both methods automatically and shows exact results.
Two Ways to Count Months Between Dates
There is no single universally agreed-upon way to count months between dates, because months themselves are irregular. The two most common approaches are:
1. Calendar-Month Counting
This method counts the number of times the calendar flips from one month to the next. It is the most intuitive approach and the one used in everyday language. For example, from January 10 to April 10 is 3 calendar months, even though January has 31 days, February has 28 (or 29), and March has 31.
If the end day is earlier than the start day within the final month, the last month is counted as partial. For example, January 20 to April 10 is 2 months and 21 days.
2. Average-Month Method
This method divides the total number of days between the two dates by 30.44 (the average number of days in a Gregorian month). It is useful for scientific, financial, and statistical purposes where a uniform month length is needed.
Formula: Months = Days Between ÷ 30.44
This is the same 30.44-day figure derived from the Gregorian calendar leap-year cycle: 365.2425 days per year ÷ 12 months = 30.44 days per month.
Step-by-Step Calculation Example
Let us calculate the months between March 5, 2025 and November 18, 2025 using both methods.
Calendar-Month Method
- From March 5 to April 5 = 1 month
- April 5 to May 5 = 2 months
- May 5 to June 5 = 3 months
- June 5 to July 5 = 4 months
- July 5 to August 5 = 5 months
- August 5 to September 5 = 6 months
- September 5 to October 5 = 7 months
- October 5 to November 5 = 8 months
- November 5 to November 18 = 13 additional days
Result: 8 months and 13 days
Average-Month Method
- Count total days: March has 26 remaining days (31 − 5) + April (30) + May (31) + June (30) + July (31) + August (31) + September (30) + October (31) + 18 days in November = 258 days
- Divide by 30.44: 258 ÷ 30.44 ≈ 8.47 months
Both methods produce similar results, but the calendar method gives an exact month-and-day breakdown while the average method gives a decimal approximation.
Common Day Counts Converted to Months
This table converts frequently referenced day counts to approximate months using the 30.44-day average.
| Days | Approx. Months | Common Name |
|---|---|---|
| 30 | 0.99 | ~1 month |
| 60 | 1.97 | ~2 months |
| 90 | 2.96 | ~3 months (1 quarter) |
| 120 | 3.94 | ~4 months |
| 180 | 5.91 | ~6 months (half year) |
| 270 | 8.87 | ~9 months |
| 280 | 9.20 | Full-term pregnancy |
| 365 | 11.99 | ~12 months (1 year) |
| 730 | 23.98 | ~24 months (2 years) |
Notice that 365 days is 11.99 months—not exactly 12—because the average month is slightly longer than 30 days. For calendar-exact counting, the date calculator is the most reliable tool.
When You Need to Count Months Between Dates
Age Calculation
Pediatricians track infant development in months for the first two years of life. A baby born on September 15 who reaches January 15 is exactly 4 months old. Our date calculator can determine a child's exact age in years, months, and days.
Contract and Lease Terms
Lease agreements, employment contracts, and subscription services are almost always stated in months. If you need to verify that a 6-month lease starting February 1 actually ends on August 1 (not July 31), calendar-month counting is the method to use.
Pregnancy Tracking
While doctors track pregnancy in weeks, many expectant parents prefer to think in months. A full-term pregnancy of 40 weeks is approximately 9.2 months. The American College of Obstetricians and Gynecologists (ACOG) provides clinical guidelines based on week counts, but month-based summaries are common in patient-facing materials. See our weeks to months conversion guide for a detailed breakdown.
Loan and Mortgage Amortization
Mortgages and auto loans are structured around monthly payments. A 30-year mortgage is 360 months; a 5-year car loan is 60 months. Knowing the number of months between your start date and a target payoff date helps you calculate remaining payments and total interest.
Statute of Limitations
Legal deadlines are sometimes expressed in months. A “6-month statute of limitations” means you must file within 6 calendar months of the triggering event. Understanding whether this is measured in calendar months or average months can have real legal consequences.
Month Lengths: A Quick Reference
Because month counting depends on the actual length of each month, here is a reference table for the standard Gregorian calendar.
| Month | Days | Notes |
|---|---|---|
| January | 31 | |
| February | 28 or 29 | 29 in leap years |
| March | 31 | |
| April | 30 | |
| May | 31 | |
| June | 30 | |
| July | 31 | |
| August | 31 | |
| September | 30 | |
| October | 31 | |
| November | 30 | |
| December | 31 |
A leap year occurs every 4 years, except for years divisible by 100 (unless also divisible by 400). The next leap year is 2028. Learn more about the leap-year rule on Wikipedia.
Frequently Asked Questions
Count the number of full calendar months from the start date to the end date, then add any remaining days as a partial month. Alternatively, count the total days and divide by 30.44 for an approximate decimal result. Our calculator does both automatically.
Not exactly. Only four months (April, June, September, November) have exactly 30 days. Seven months have 31 days, and February has 28 or 29. The average month is 30.44 days, so 30 days is approximately 0.99 months.
90 days is approximately 2.96 months (90 ÷ 30.44). In calendar terms, this is roughly 3 months, though the exact count depends on which specific months are involved.
The discrepancy usually comes from using different methods. Some calculators use the average-month method (dividing by 30.44), while others use calendar-month counting. They may also differ on how partial months at the start and end of the range are handled.
One calendar year is exactly 12 months. Using the average-month method, 365 days ÷ 30.44 = 11.99 months, which rounds to 12. A leap year (366 days) gives 12.02 months by the same method.
Pediatricians use calendar-month counting. A baby born on March 10 turns 1 month old on April 10, 2 months on May 10, and so on. This continues through the first 24 months, after which age is typically given in years.