Guides

In-depth explainers that go beyond the calculators: how the formulas work, where the numbers come from, and how to apply them to your own decisions. Every guide links to the tools that let you run the math yourself.

• Compound Interest Explained

  How compounding actually works: the formula, the rule of 72, why starting early beats saving more, and what fees quietly cost you over decades.

  Daniel Mercer, CFP® · Last reviewed July 15, 2026

• Debt Snowball vs. Avalanche: Which Is Right for You?

  Snowball and avalanche compared with real numbers: how each works, the true interest difference, and how to pick the plan you'll actually finish.

  Daniel Mercer, CFP® · Last reviewed July 15, 2026

• How Mortgage Payments Are Calculated

  The amortization formula behind every mortgage payment, explained step by step — worked example, PITI breakdown, and what extra payments really do.

  Daniel Mercer, CFP® · Last reviewed July 15, 2026

• The 4% Rule and FIRE, Explained

  Where the 4% rule comes from, what the Trinity study really found, how the 25× savings target works, and how your savings rate sets your retirement date.

  Daniel Mercer, CFP® · Last reviewed July 15, 2026