Guides
How the arithmetic behind money decisions actually works — with the numbers shown.
Each guide explains one financial mechanism end to end: what the formula is, where the money goes, and the assumptions that change the answer. They are written to be read alongside the calculators, not instead of them.
How a Mortgage Payment Actually Works
Most of your first payment is not your house. Here is where each dollar goes, and why the split moves so slowly that the loan feels frozen for years.
10 min read
Fixed vs Adjustable Rate: The Break-Even Math
The adjustable loan hands you a smaller payment and a larger risk. The only question that decides it is how long you will actually be in the house.
10 min read
When Refinancing Actually Pays Off
Divide closing costs by the monthly savings and you get a number. It is the wrong number, and the error usually runs into five figures.
10 min read
Compound Interest, With the Numbers Shown
The formula fits on one line. What it does across thirty years does not fit in your intuition, which is why the tables below are worth more than the rule of thumb.
10 min read
Roth vs Traditional IRA: The 2026 Decision
Almost everything written about this choice is a guess about a tax rate you will not know until decades from now. Here is the part that is not a guess.
10 min read
How Much You Actually Need to Retire
The number you need is not a round figure from a magazine. It is a function of what you spend, what Social Security replaces, and how long the money has to last.
10 min read
Snowball vs Avalanche: The Real Difference
Both methods use the same money and the same debts. The only variable is which balance receives the extra payment, and that one choice is worth about $198 in the example below.
10 min read
APR vs Interest Rate: What the Loan Offer Does Not Say
The APR is a better number than the interest rate and still not the number you need. Here is what it includes, what it conceals, and how to compute the cost the disclosure never states.
10 min read
How Big Should Your Emergency Fund Be?
Three to six months of income is the slogan. Your actual number comes from essential expenses, how fragile your income is, and the specific bad months that are likely to happen to you.
10 min read
The Rule of 72, and When It Lies to You
Divide 72 by a growth rate and you get the years it takes to double your money. The trick is accurate to a few weeks at 7% and off by months at 30%, and the error has a shape you can learn.
9 min read