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The ideas behind the numbers
Five short pieces explaining what the calculators are doing and where they stop being trustworthy. No opinions on what you should buy — this site does not have any, and anyone who offers you one for free usually has a reason.
- What compounding actually isThe one idea the whole site rests on, explained without the snowball metaphor.
- Returns are not a straight lineWhy every calculator on the internet — including this one — draws a curve that will not happen, and what to do about it.
- What an index fund isA plain description of the thing, with no opinion about whether you should own one.
- Fees, explained properlyExpense ratios, platform charges and the reason a percentage is the wrong unit to think in.
- A short glossaryTwenty-odd terms you will hit in your first month, defined in one line each.
- Is a 3% raise good? Do the arithmetic"Good" is not a feeling. It is a comparison with inflation and tax, and it takes about a minute.
- How much more should a contractor make?There is no single percentage. There is a sum, and the biggest part of it is days you cannot bill.
- T-bills vs high-yield savings, after taxComparing the two headline rates is the wrong sum for anyone who pays state income tax. Here is the right one.
- Why is my credit card minimum payment going up?A minimum normally shrinks as you pay the card down. When it grows instead, something specific changed.
- Why is most of my mortgage payment interest?Nobody front-loaded anything. Interest is charged on what you still owe, and at the start you owe almost all of it.
- Marginal tax rate vs effective tax rateOne is the rate on your next dollar, the other is the average on all of them. Mixing them up is where the bracket myth comes from.
- Should I overpay my mortgage or invest?The arithmetic has exactly one break-even point, and it is printed on your mortgage statement. Everything else is a question about risk.
- Lump sum vs dollar-cost averaging: the real gapSpreading a windfall in has a price. It can be measured, it is usually smaller than the argument about it, and it buys something real.
- Is the 4% rule still valid?It was never a forecast. It was the worst case in one country’s history, under assumptions most people never read.
- Debt snowball vs avalanche: which is better?On interest alone the avalanche almost always wins. The useful question is by how much, and that depends on your debts.
- APR vs APY: what each rate actually countsOne is a yearly rate before compounding, the other after it. Which one you are shown depends on whether you are borrowing or saving.
- What CAGR actually measuresOne steady rate that links a start value to an end value. It is honest about the destination and silent about everything in between.
- Nominal vs real return: which one to useOne counts dollars, the other counts what dollars buy. Both are correct. The mistakes come from mixing them in the same sum.
- Why is the first 100k the hardest?The saying is true for most savers, and the arithmetic says exactly why. It also says who it is not true for.
- How much should I save?Any one-size answer is a rule of thumb built around somebody else. Yours is a sum, worked backwards from the goal.