Guides
Short, plain-English explainers for the math behind our calculators — so you understand the result, not just the number.
How Mortgage Payments Work
Understand what makes up a mortgage payment, the amortization formula, and how to pay less interest over the life of the loan.
Read guide →Compound Interest, Explained Simply
How compound interest works, why starting early matters so much, and how regular contributions accelerate growth.
Read guide →Understanding Your BMI
What Body Mass Index measures, how to read the categories, and the limits of BMI as a health metric.
Read guide →How to Calculate Percentages
The three percentage questions that come up most — percent of a number, percentage change, and what percent one number is of another.
Read guide →Daily Calories and TDEE, Explained
The difference between BMR and TDEE, how activity multipliers work, and how to set calories for losing or gaining weight.
Read guide →How US Federal Income Tax Works
Marginal vs effective tax rates, the standard deduction, and why moving into a higher bracket doesn't tax all your income.
Read guide →