CalcKit

Guides

Formulas and rounding rules for tip, margin, and percentage.

• How a tip calculator splits a bill

  Tip amount, total, and per-person rounding — the same math CalcKit uses.

• Margin vs markup

  Why 25% margin is not 25% markup, and how sell price is derived from cost.

• Three percentage problems

  X% of Y, “what percent is X of Y”, and percent change — including zero and negatives.