Calculate a discount—including an extra discount
Learn the two-step method and check what sequential promotions actually change.
Read the guide →Practical calculation guides
Learn the method behind the number.
Original guides for everyday percentage and time-zone questions. We show workings, state assumptions, and avoid turning a calculator into financial, tax, or professional advice.
Percentage points vs percentage change
A clear guide to a distinction that matters whenever a rate moves.
Read the guide →School and project percentages
Use parts, totals, weights, and progress figures accurately.
Read the guide →Plan meetings across time zones
Convert time correctly, then schedule with the people involved in mind.
Read the guide →Our approach
Published by Alnto Tsekou, these guides begin with a practical question a visitor can solve. We explain the formula, show examples, identify edge cases, and link to methodology and sources. Read the editorial policy or send a correction.