Days Between Dates Calculator Formula

Understand the math behind the days between dates calculator. Each variable explained with a worked example.

Use the Days Between Dates Calculator

Formulas Used

Approximate Days

approx_days = month_diff * 30.44

Approximate Weeks

approx_weeks = month_diff * 30.44 / 7

Months Between

months_between = month_diff

Variables

VariableDescriptionDefault
start_yearStart Year2025
start_monthStart Month (1-12)1
end_yearEnd Year2026
end_monthEnd Month (1-12)3
month_diffDerived value= (end_year - start_year) * 12 + (end_month - start_month)calculated

How It Works

How to Estimate Days Between Dates

Using the average month length (30.44 days = 365.25/12), multiply by the total months between two dates.

Formula

Days = Month Difference x 30.44

This gives an approximation; actual days vary by month length and leap years.

Worked Example

From January 2025 to March 2026.

start_year = 2025start_month = 1end_year = 2026end_month = 3
  1. 01Month difference = (2026 - 2025) x 12 + (3 - 1) = 14
  2. 02Approximate days = 14 x 30.44 = 426
  3. 03Approximate weeks = 426 / 7 = 60.9

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