Money & Math Guides
Worked-example explanations of the money and math behind the calculators — debt payoff, compound interest, APR, pay raises, tipping and GPA. Real numbers, not just formulas.
How to Calculate a Pay Raise Percentage
The three-step formula, then the part most raise conversations skip: with inflation at 3.4%, a 3% raise is a pay cut.
Read the guide →Tip vs. Sales Tax: How They Actually Differ
One is set for you, the other is yours — and the payment terminal quietly picks the higher base, costing about 8% more tip than you meant to leave.
Read the guide →How to Calculate Your GPA Using Percentages
Percentage grades to grade points, including a full weighted example — and why your heaviest classes, not your worst ones, are where effort actually moves the number.
Read the guide →Debt Snowball vs. Avalanche: What the Difference Actually Costs
Everyone says avalanche is cheaper. This shows how much cheaper — two worked examples where the same choice costs $344 in one case and $24 in the other, plus what the research says about which method people actually finish.
Read the guide →Understanding Compound Interest
Interest earning interest, with real numbers — and the direction nobody charts: at today’s card rates, an untouched balance roughly doubles in three years.
Read the guide →APR vs. Interest Rate: What’s the Difference?
Two numbers on every loan quote that look alike and aren’t — plus the assumption inside APR that makes high-fee loans look better than they are.
Read the guide →