Category: Calendar Math

Days between birth date and today give exact age spans—useful for milestones beyond whole years.

Pure date tools ignore clock time; crossing midnight UTC vs local may shift calendar day on international trips.

Inclusive counts both endpoints; exclusive counts only full days between—contracts specify which applies.

ISO weeks start Monday; week 1 contains the first Thursday—special rules differ from casual week counting.

Adding one month is not always 30 days—use date tools instead of multiplying by 30 mentally.

366-day leap years shift anniversary and annual deadlines—calculators handle leap logic if inputs are correct.