Guides

Practical explanations with worked examples.

• How to Calculate Percentage Increase and DecreaseThe formula for percentage increase and decrease, with worked examples and the most common mistake to avoid.
• Profit Margin vs. Markup: What’s the Difference?Margin divides profit by the selling price; markup divides it by the cost. See both calculated on the same item and how to convert between them.
• How to Compare Unit Prices When ShoppingDivide price by size to find the cost per ounce, gram or item, and compare packages fairly.
• How to Calculate Work Hours With Unpaid BreaksSubtract the start time from the end time, take off unpaid breaks, and convert minutes to decimal hours for pay.
• How to Find the Original Price Before a DiscountDivide the sale price by (1 − discount) to recover the original price — and why adding the percentage back gives the wrong answer.