Free Financial & Health Guides
In-depth guides that explain the math and strategy behind our calculators. 15 guides covering finance, investing, health, and more.
💰 Finance & Investing
How Compound Interest Works
A complete beginner's guide to compound interest — the most powerful force in personal finance. Learn the formula, see real examples, and understand why starting early matters so much.
Simple vs. Compound Interest
Understand the critical difference between simple and compound interest, when each is used, and how to calculate both. Includes worked examples and comparison tables.
How to Double Your Money: The Rule of 72
Master the Rule of 72 — the mental math shortcut that lets you instantly estimate how long it takes to double any investment. Includes variations and real-world applications.
Compounding Frequency Explained
Does it matter whether interest compounds daily, monthly, or annually? This guide breaks down the math and shows exactly how much difference compounding frequency makes.
APR vs. APY: What's the Difference?
Banks use APR and APY strategically to make products look better. Learn the difference, how to convert between them, and how to use this knowledge to make smarter financial decisions.
Understanding Mortgage Amortization
Learn how mortgage amortization works, why you pay mostly interest at the start, how to read an amortization schedule, and strategies to pay off your mortgage faster.
Retirement Planning: How Much Do You Really Need?
A comprehensive guide to retirement planning — how to calculate your retirement number, the 4% rule, account types, and strategies to retire on your terms.
Break-Even Analysis: What It Is and How to Use It
Learn how to calculate your break-even point, understand fixed vs. variable costs, and use break-even analysis to make smarter business and pricing decisions.
❤️ Health & Wellness
Understanding BMI: What It Means and Its Limitations
A complete guide to Body Mass Index — how it's calculated, what the categories mean, why it's useful, and where it falls short as a health measure.
Understanding Macros: A Complete Guide to Macronutrients
Learn what macronutrients are, how many calories each contains, how to calculate your ideal macro split, and how to use macros to reach your health and fitness goals.
Body Fat Percentage: What It Means and How to Reduce It
How body fat percentage is measured, healthy ranges for men and women, how it differs from BMI, and evidence-based strategies to reduce it.
What Is BMR? Your Basal Metabolic Rate Explained
Learn what BMR is, how it's calculated using the Mifflin-St Jeor equation, how it differs from TDEE, and how to use it to set accurate calorie goals.
How Much Water Should You Drink Per Day?
A science-backed guide to daily water intake — how much you actually need, factors that affect requirements, signs of dehydration, and practical hydration tips.
Sleep Science: How Much Sleep Do You Need and How to Get It
How much sleep you need by age, what happens during sleep cycles, the real cost of sleep deprivation, and evidence-based strategies to improve sleep quality.
Running Pace Guide: How to Calculate, Train, and Race Smarter
Everything about running pace — how to calculate it, training zones, how to set realistic race goals, and how to use pace-based training to run faster.