Months Calculator
A powerful tool to calculate time spans, add or subtract months from a date with precision.
Operation Type
Result
Your result will appear here.
How to Use This Calculator
Select Operation
Choose 'Months Between', 'Add Months', or 'Subtract Months' to begin.
Enter Dates
Use the calendar pickers or the 'Today' buttons to input your dates and values.
Calculate & View
Click 'Calculate' to see the detailed result, including a visual timeline.
The Logic of Month Calculation
Calculating months isn't as simple as it sounds due to varying month lengths (28, 29, 30, or 31 days). Our calculator uses a precise method:
- It calculates the total number of full years and full months between the dates first.
- It then calculates the remaining days, carefully handling "borrowing" from months and years to ensure accuracy.
- For adding/subtracting, it correctly adjusts for end-of-month dates (e.g., adding 1 month to Jan 31 results in Feb 28/29).
Fun Facts About the Months
Roman Origins
September, October, November, and December mean 7th, 8th, 9th, and 10th month in Latin, from the old Roman calendar which started in March.
Leap Year Logic
A leap year occurs every 4 years, except for years divisible by 100 but not by 400. This keeps our calendar aligned with the Earth's orbit.
The Only One
February is the only month that can pass without a full moon, a phenomenon known as a "black moon". This happens roughly every 19 years.
Months in Business & Finance
Time calculations are critical in the professional world. Use this calculator for:
Frequently Asked Questions
By default, the calculation does not include the end day (e.g., Jan 1 to Jan 2 is 1 day). Checking this box adds one full day to the total duration before calculating the months and days.
Yes. The underlying JavaScript Date objects automatically account for leap years (e.g., February having 29 days) when performing calculations, ensuring accuracy.