How to Calculate Days Between Two Dates
Calculating the exact number of days between two dates is harder than it looks because months have different lengths, years have 365 or 366 days, and the question of whether to count start and end dates varies by context.
The Julian Day Number approach
The most reliable way to count days between dates is to convert both to a Julian Day Number (a sequential count of days from a fixed starting point), then subtract. This handles leap years and month-length differences automatically. The date difference calculator uses this method to give you an exact count instantly.
Calendar days vs. business days
Calendar days count every day including weekends. Business days exclude Saturdays and Sundays (and sometimes public holidays). "5 business days" from Monday is the following Monday, not Saturday. If you are counting deadlines, invoice due dates, or shipping timelines, clarify which type of day applies.
Common use cases
Countdowns to events: enter today's date and a future date. Age verification: enter a birth date and today. Elapsed time: enter a start date and end date to find project duration. Contract deadlines: add a number of days to a contract signing date to find the due date.