Guides

The calculators give you a number. These guides explain where the number comes from, what it leaves out, and how to use it without fooling yourself.

• How Compound Interest Actually Works, With Real Numbers

  Compound interest is easy to explain and hard to feel. What $10,000 and $200 a month turn into over 10, 20 and 30 years, and why the early years look so unimpressive.

  5 min read

• BMI Explained: What the Number Can and Can't Tell You

  BMI is a quick ratio of weight to height, nothing more. Where it came from, how to read it, who it misleads, and what to look at alongside it.

  4 min read

• Reading Your Paycheck: Where the Money Goes Before You See It

  A line-by-line walk through a $75,000 salary: what comes out for payroll taxes, a 401(k) and federal income tax, and why your deposit is smaller than the offer letter.

  5 min read

• Mortgage vs. Rent: The Real Monthly Math

  Buying and renting aren't as different on paper as people assume. What actually changes month to month, and the costs that never show up in either number.

  4 min read