The arithmetic behind the advice
Every guide here is built on a number you can reproduce in one of the calculators. Where the conventional wisdom does not survive the data, that is said plainly rather than smoothed over.
The Lost Decade: What a Ten-Year Return Can Actually Look Like
Between March 1999 and February 2009, the S&P 500 lost 5.44% a year for ten straight years. Here is what every overlapping ten-year window in the real data says about the range of outcomes.
Your Fund Beat the Market. That Is Not the Same as Being Good
A fund returned 15% while the index returned 10%. Whether that is skill or leverage depends entirely on one number, and the arithmetic that separates them takes about thirty seconds.
What Happens When You Test a Trading Strategy Honestly
Three textbook strategies, run against real S&P 500 history with the parameters frozen before the test. All three beat nothing. Here is why that is the normal result.
Daily Compounding Is Not the Advantage You Think It Is
Over thirty years, switching from annual to daily compounding on $10,000 adds about 5%. Adding $100 a month adds about 170%. The banks advertise the first one.
The Month Your Credit Card Balance Starts Growing
On $8,500 at 22% APR, the interest alone is $155.83 in the first month. Pay less than that and the balance climbs no matter how long you keep paying.