Definition
Inclusive day count
An inclusive day count includes both the first and the last day of a range, so from the 3rd to the 10th is eight days rather than seven.
Most people count inclusively when they talk about dates, and most contracts do too. Knowing which convention you are using is what prevents the off-by-one error.
Tools that use this term
Date Difference Calculator
Days, weeks, months and working days between two dates, counted both ends.
Countdown Calculator
How much time is left before a date, in days, weeks and working days.
Work Hours Calculator
Hours worked from a start and end time, with the break deducted, per day and per week.