Everyday Math & Text
How to Figure Discounts, Sales Tax and Tips in Your Head
One trick covers most shopping math: find 10% first. Here's how to price discounts, add sales tax and pick a tip in your head, and why stacked discounts mislead.
Everyday Math & Text
Percentages, loans, dates and text limits, explained with worked examples.
Everyday Math & Text
APR vs Interest Rate: What's the Difference?
The interest rate sets your monthly payment. The APR folds points and lender fees into one yearly rate. Here's how it's calculated and when it misleads.
Everyday Math & Text
How to Count Days Between Dates (Inclusive or Not)
Monday to Friday is 4 days or 5, depending on how you count. Here's when to include the end date, how to count business days, and how legal deadlines are counted.
Everyday Math & Text
SMS Character Limits: Why 160 Becomes 70
A single emoji or curly apostrophe can cut an SMS limit from 160 characters to 70 and double the cost. Here's how SMS encoding and segments work, with real examples.
Everyday Math & Text
How Loan Amortization Works (and What Extra Payments Save)
Why early mortgage payments go mostly to interest, how the payment formula works, and what extra payments really save, worked through on one $300,000 loan.
Everyday Math & Text
Percent Change vs Percentage Points
A rate going from 4% to 5% rose by 1 percentage point, or by 25%. Here's how to calculate each, when to use which, and the mistakes that make numbers misleading.