Guides & Comparisons
In-depth articles to help you understand the numbers behind our calculators.
BMI vs Body Fat: Which Metric Actually Matters?
BMI is quick but flawed. Body fat tells the real story. Here's when each matters.
FinanceMarkup vs Margin: The Difference That Costs Thousands
Markup and margin are not the same. Confuse them and you'll misprice everything.
FinanceDebt Snowball vs Avalanche: Which Payoff Strategy Wins?
Snowball builds momentum. Avalanche saves money. Which payoff strategy actually works?
FinanceAPY vs APR: What Your Bank Doesn't Explain
APY and APR both describe rates — but one includes compounding and one doesn't.
MathHow to Calculate Percentage: 3 Methods Anyone Can Use
Three simple methods for percentages: of a number, between values, and change.
FinanceHow to Calculate Compound Interest (With Real Examples)
The compound interest formula explained with real dollar examples and savings scenarios.
Baby & ParentingHow Much Does a Baby Cost in the First Year?
From diapers to daycare — a real cost breakdown for your baby's first year.
Baby & ParentingBaby Growth Percentiles: What the Numbers Mean
Growth percentiles confuse parents. Here's what the numbers actually mean.
FinanceAnnuity vs Linear Mortgage: Which Saves You More?
Two repayment systems, same loan. One saves money, the other simplifies budgeting. Here's how they compare.
FinanceWhen to Refinance Your Mortgage: A Break-Even Guide
A lower rate doesn't always mean you should refinance. Here's how to calculate your break-even point.
FinanceHow Extra Mortgage Payments Save You Thousands
Even small extra payments can save you tens of thousands. Here's the math behind overpaying your mortgage.
HealthUS Navy Body Fat Calculator: How the Official Method Works
The Navy's tape test has measured sailors since 1981. Here's exactly how the Hodgdon-Beckett method works.
HealthArmy Body Fat Standards (AR 600-9): Complete 2026 Guide
AR 600-9 and ALARACT 087/2025 changed how the Army measures body fat. Here's what soldiers need to know.
HealthUSMC Body Fat Standards (MCO 6110.3): Marines Tape Test Guide
The Marine Corps holds the tightest body fat standards in the US military. Here's how MCO 6110.3 works.
HealthArmy vs Navy vs Marines Body Fat Standards Compared
The three major US branches use different body fat limits. Here's the side-by-side.
HealthHow to Pass a Military Tape Test: Prep, Technique, Mistakes
The tape test has ended careers. Here's how to prep, what to do on test day, and the mistakes that get people flagged.
HealthTape Test vs DEXA Scan: Why the Military Uses Tape
DEXA is more accurate, so why does the military still use a cloth tape? The trade-offs are bigger than they look.
MathHow Accurate Are Quick IQ Tests? The Science of Short Assessments
Short IQ tests are everywhere online. Here's what the science says about their accuracy and limits.
MathThe Wechsler IQ Test: History, Methodology, and Modern Use
David Wechsler's scale has defined modern IQ testing since 1955. Here's how it actually works.
MathMensa Qualification Guide: Scores, Tests, and How to Join
Mensa accepts members at the 98th percentile. Here's exactly what that means and how to qualify.
MathRaven's Progressive Matrices: The 1936 Test That Still Works
John C. Raven invented his matrix test in 1936. Ninety years later, it's still one of the most-used IQ assessments.
MathCulture-Fair IQ Tests: Measuring Intelligence Across Cultures
Raymond Cattell designed the first culture-fair test in the 1940s. The concept is still important — and still imperfect.
MathEvery IQ Test Type Compared: Mensa, Raven's, Wechsler, and More
Mensa, Wechsler, Raven's, culture-fair: the major IQ tests side-by-side, with the trade-offs explained.
MathHow IQ Scoring Works: The Bell Curve, Z-Scores, and Percentiles
An IQ of 115 means something specific — and it has nothing to do with intelligence being measured directly.
MathThe Flynn Effect: Why Average IQ Scores Have Been Rising for a Century
Average IQ scores have been rising for 100 years. The reason has nothing to do with getting smarter.
HealthWhat Is TDEE and How Do You Calculate It?
TDEE is the total calories you burn per day. Here's how to calculate yours.
HealthTDEE vs BMR: What's the Difference and Which Should You Use?
BMR is calories at rest. TDEE is calories in a day. Here's when each matters.
HealthHow to Calculate Calorie Deficit for Weight Loss (Step by Step)
Step-by-step: find your TDEE, subtract 500, and track progress.
HealthBest Macro Split for Weight Loss vs Muscle Gain
The best macro split depends on your goal. Here's what the research says.
HealthHow Many Calories Should I Eat to Lose 1 Pound Per Week?
A 500 cal/day deficit = 1 lb/week. Here's how to make it work.
HealthAre TDEE Calculators Accurate? What the Research Says
TDEE formulas are estimates, not gospel. Here's how accurate they really are.