Month Calculator
Calculate the exact number of months between any two dates, or count months from today to any upcoming or past event — free and instantly.
Last updated: March 2026
How to Use the Month Calculator
- Select a mode — Use "Months Between Dates" to measure the month gap between any two calendar dates, or "Months From Today" to count months until or since a specific event.
- Enter your dates — Click the date pickers or type dates directly. "Months From Today" uses today's date automatically as the start.
- Read results instantly — You'll see complete calendar months, remaining days, total days, total weeks, and decimal months. Results update immediately as you type.
- Share or clear — Click Share to copy a pre-filled link, or Clear to start over with new dates.
How the Month Calculator Works
Calculating months is more nuanced than calculating days or weeks, because months have different lengths. The calculator uses a day-aligned calendar-month algorithm rather than a simple division of total days.
The Core Algorithm
Given start date S and end date E (ensuring S <= E):
- Compute the raw month difference: (E.year − S.year) × 12 + (E.month − S.month)
- If E.day < S.day, subtract one month (the last month is not yet complete) and calculate remaining days from the last complete month boundary to E
- Remaining days = E.day − S.day (or a positive equivalent crossing a month boundary)
This approach matches how humans intuitively count months: from January 15 to April 10 is 2 complete months (Jan 15 → Feb 15 → Mar 15) with 26 remaining days (Mar 15 → Apr 10).
Worked Examples
- Subscription duration: Mar 1, 2025 to Mar 4, 2026 → 12 months, 3 days
- Pregnancy from LMP: Oct 10, 2025 to Jul 4, 2026 → 8 months, 24 days
- Lease term: Sep 1, 2025 to Aug 31, 2026 → 11 months, 30 days
- Baby age: Born Nov 15, 2025 to Mar 4, 2026 → 3 months, 17 days
Why Count in Months?
Months are deeply embedded in how we structure financial, medical, and personal milestones. Unlike weeks (which ignore calendar structure) or days (which are too granular for long-range planning), months align with billing cycles, interest periods, lease terms, and developmental checkpoints.
Finance and billing operate on a monthly cadence: rent, mortgages, subscriptions, loan payments, and insurance premiums are all priced per month. Knowing the exact number of months in a contract period — including the leftover days — determines the total cost and pro-rated amounts for partial months.
Baby development is tracked in months for the first two years of life. Pediatricians ask "how old is your child in months?" rather than weeks or years, because developmental milestones — sitting, crawling, first words — are defined by month. A child's age in months is the standard clinical unit until age 24 months.
Loan amortization schedules are built on monthly periods. A 30-year mortgage is 360 monthly payments. Calculating how many months remain on a loan, or how many months of interest have accrued, requires precise month counting that accounts for the different lengths of calendar months.
Pregnancy uses both weeks and months. While medical tracking is in weeks, most expectant parents think in months ("I'm 7 months pregnant"). The calculator bridges both: it shows months, weeks, and days simultaneously.
Months in Common Time Periods
Understanding how months relate to other time units:
- 1 quarter = 3 months (Q1: Jan–Mar, Q2: Apr–Jun, Q3: Jul–Sep, Q4: Oct–Dec)
- Half year = 6 months
- Full year = 12 months = approximately 52.18 weeks = 365.25 days average
- 18 months = 1 year 6 months ≈ 547–548 days
- Pregnancy (full term) = 9 months 1 week = 40 weeks = 280 days
- US lease (standard) = 12 months = 365 or 366 days
- Probationary period (common) = 3 months = about 91 days
How Many Months If...
How many months between January 1 and December 31?
There are 11 complete months and 30 days between January 1 and December 31. January 1 to December 1 is exactly 11 months; December 1 to December 31 is 30 additional days. The full calendar year from Jan 1 to Jan 1 (next year) is exactly 12 months.
How many months is 365 days?
365 days is approximately 12 months (one full year). More precisely, using the average month of 30.44 days: 365 ÷ 30.44 ≈ 11.99 months. For calendar-accurate results, enter exact start and end dates — a 365-day period may span 11 or 12 calendar months depending on which months are included.
How many months until July 4th?
From March 4, 2026, there are exactly 4 months until July 4, 2026. March 4 to April 4 (1 month), April 4 to May 4 (2 months), May 4 to June 4 (3 months), June 4 to July 4 (4 months). Zero remaining days.
How many months old is a baby born 6 months ago?
A baby born 6 months ago is 6 months old. Use "Months From Today" mode and enter the baby's birth date. The complete months result is the child's age in months, which is the standard measurement used by pediatricians through the first 24 months.
How many months is a 2-year lease?
A 2-year lease is 24 months. If the lease spans two calendar years with a February 29 (leap year), the total day count may be 730 or 731 days, but the month count remains exactly 24 complete months from the same day-of-month in the start and end years.
How many months between March and October?
From March 1 to October 1, there are exactly 7 months. Month by month: March→April→May→June→July→August→September→October = 7 steps. If you count from March 1 to October 31, that is 7 months and 30 days.
How many months is 180 days?
180 days is approximately 5 months and 28 days to 6 months, depending on the starting month. Using the average: 180 ÷ 30.44 ≈ 5.91 months. A 180-day period starting on March 1 ends on August 28 (5 months, 27 days). Starting on April 1 ends September 28 (5 months, 27 days).
How many months pregnant am I if my LMP was 5 months ago?
If your last menstrual period (LMP) was 5 months ago, you are approximately 5 months pregnant, which corresponds to roughly 20–22 gestational weeks. At 5 months pregnant, you are in the second trimester. Enter your exact LMP date in the calculator for a precise count in months, weeks, and days.
People Also Search For
How to calculate months between dates in Excel
In Excel, use the DATEDIF function: =DATEDIF(A1, B1, "M") returns the complete months between dates in A1 and B1. For remaining days after complete months: =DATEDIF(A1, B1, "MD"). Note: DATEDIF is an undocumented legacy function but works in all modern Excel versions. Alternatively, use =YEARFRAC(A1, B1)*12 for decimal months.
How to count months for subscription billing
For subscription billing, count from the billing start date to the cancellation or end date using calendar months. Enter the subscription start date and the end or cancellation date. The complete months count is the number of full billing cycles. Any remaining days typically constitute a pro-rated partial month charge.
How many months since a specific date
Use "Months From Today" mode and enter the past date as your target date. If the target is before today, the calculator still works — it computes the absolute difference. The result shows how many complete months have passed since that date, useful for tracking anniversary milestones, subscription ages, or tenure.
How to calculate age in months
Enter the birth date as the start date and today (or any reference date) as the end date in "Months Between Dates" mode. The complete months result is the age in months. This is the standard pediatric measurement for children under 2 years and is also used in developmental screening and growth chart plotting.
How many months is a standard mortgage term?
A 15-year mortgage is 180 months; a 30-year mortgage is 360 months. Each monthly payment covers one month of amortization. Mortgage calculators use these month counts to build amortization schedules. If you make extra payments, you reduce the remaining month count — use this calculator to see how many months remain after prepayments.
Frequently Asked Questions
How do I calculate the number of months between two dates?
Subtract the year and month of the earlier date from the later date: (years difference × 12) + months difference. If the end day is before the start day, subtract one month and add the leftover days. The calculator handles this automatically.
How many months are in a year?
There are exactly 12 months in a year. The months vary from 28 days (February in a non-leap year) to 31 days. The average month length is approximately 30.44 days (365.25 ÷ 12).
How many months is 90 days?
90 days is approximately 2 months and 28–30 days depending on which months are included. Using the average month (30.44 days), 90 ÷ 30.44 ≈ 2.96 months. For an exact answer, enter specific dates into the calculator.
Can this calculate baby age in months?
Yes. Enter the baby's birth date as the start and today as the end in "Months Between Dates" mode. The complete months result is the child's age in months — the standard pediatric measurement used through the first 24 months.
What is a decimal month?
A decimal month expresses the fractional part of a month as a decimal: for example, 3 months 15 days ≈ 3.5 months (using a 30-day month approximation). The calculator shows total days divided by 30.44 (the average month) as the decimal month figure.
Does the calculator account for different month lengths?
Yes. The complete months calculation uses a calendar-aligned algorithm that correctly handles months of 28, 29, 30, and 31 days, including leap year Februaries. The remaining days figure reflects the actual days in the partial month at the end of the period.
How do I use this for lease or contract terms?
Enter the lease start date and end date in "Months Between Dates" mode. The complete months count shows the number of full calendar months in the term. Note that lease agreements sometimes define month-end clauses differently — always check your contract for exact billing terms.
Can I calculate months for past dates?
Yes. Enter any historical start and end dates. The calculator returns the absolute month difference so order doesn't matter. This is useful for calculating subscription ages, how long a contract has been active, or the months since any milestone.
Is my data private?
All calculations run entirely in your browser. No dates are sent to any server, and nothing is stored or logged. Your inputs are completely private.
How many months is 1 year and 6 months?
1 year and 6 months is exactly 18 months. This is a common tenure milestone in employment, a standard probation extension period, and the typical age when many toddler developmental checkups occur. As days: 18 months ≈ 547–548 days depending on leap year overlap.