Guides
Each guide picks up a question one of our calculators raises and works through it with real numbers. Official figures are linked to the agency that publishes them, and every worked example matches what the calculator shows.
Interest rates and loans
Flat-Rate Loans: How to Find the Real Interest Rate
Why "1% a month flat" costs about 21.5% a year, and how to work out the real rate of any flat-rate or add-on loan.
Read the guide →Compound Interest Explained, With Worked Examples
The formula in plain English, how compounding frequency and regular savings change the result, and the rule of 72.
Read the guide →Insurance
How the ACA Premium Tax Credit Works for 2027 Coverage
The 2026 poverty guidelines, the IRS percentages for 2027, the benchmark Silver plan and the 400% cliff, step by step.
Read the guide →How Much Term Life Insurance Do You Need?
A needs-based calculation that goes past the five-times-income rule, plus how term length and laddering change the price.
Read the guide →Retirement
The 4% Rule: What It Assumes and When It Breaks
Where the rule comes from, how the Retirement Runway Calculator uses it, and why bad early years matter so much.
Read the guide →When to Claim Social Security: 62, 67 or 70
How the claiming age changes your benefit, the break-even ages, and the 2026 and 2027 earnings test limits.
Read the guide →