Money & Math Guides

Short, practical explainers on the math behind everyday decisions — written to be read in five minutes, with calculators one click away.

• Mortgage Basics: How Your Monthly Payment Really Works
  Principal, interest, taxes, insurance, and PMI — what actually goes into a house payment, and how to compare offers like a lender does.
  Updated 2026-10-11
• BMI, Body Fat, and What "Healthy Weight" Actually Means
  BMI is a screening tool, not a verdict. How BMI, body fat percentage, and ideal-weight formulas fit together — and which number to watch.
  Updated 2026-10-11
• Percentages Without Panic: The Five Formulas You Actually Need
  Percent of, percent change, percent difference, percent off, and percent error — when to use each, with worked examples.
  Updated 2026-10-11
• Buying a Car: Loan, Lease, or Cash?
  How dealers structure deals, where trade-ins and fees hide, and the numbers that tell you which financing route is actually cheaper.
  Updated 2026-10-11
• Dates, Ages, and Durations: The Math People Get Wrong
  Inclusive counting, month-length traps, time zones, and why your age changes at midnight — the conventions behind date calculators.
  Updated 2026-10-11
• Calories, BMR, and TDEE: Where Every Number Comes From
  What BMR and TDEE actually measure, why activity multipliers vary, and how to set a deficit or surplus you can sustain.
  Updated 2026-10-11
• Getting Out of Debt: Avalanche, Snowball, and the Minimum-Payment Trap
  Why minimum payments keep you in debt for decades, which payoff order saves the most, and when consolidation helps.
  Updated 2026-10-11