Standard date difference
A standard days-between-dates calculation measures the gap from the start date to the end date. This is often what people need for elapsed time, age ranges, or simple historical comparisons.
Inclusive counting
Inclusive counting includes both the starting day and the ending day. This matters for booking ranges, campaigns, stays, deadlines, and legal or administrative windows where both boundary dates count.
Why a breakdown can help
A raw number of days is useful, but a breakdown into years, months, weeks, and days can be easier to understand in real planning. For example, 425 days may be more meaningful when expressed as 1 year, 1 month, and 29 days.