Where the numbers come from

Nothing in the guide is typed by hand. Every figure is computed by a script and checked when the book is built, drawn from a verified fact bank, verified with a source at build time, or clearly labeled as a made-up example. This is that list.

Every figure in the guide is one of four things.

1. Computed

Produced by content/math.ts at build time and checked by npm run check:math. Assumption: 10% a year, the long-run S&P 500 average, stated in the text every time it is used. Monthly contributions compound monthly; standalone lump sums compound yearly (matching the fact bank).

2. From the verified fact bank supplied with the brief

• Nasdaq-100 fell 75.85% from the March 2000 peak and did not break even until August 2013. (Rounded to "about 76%" in prose.)
• S&P 500 returned about -18% in 2022, then about +26% in 2023 and about +25% in 2024.
• COVID crash: S&P 500 fell about 34% in roughly five weeks (Feb to Mar 2020) and fully recovered in about five months.
• The S&P 500's worst five-year rolling stretch since 2010 still returned about +6.71% per year. (Rounded to "about 6.7%".)
• The S&P 500 has averaged roughly 10% a year over the long run, and has finished up roughly 3 out of every 4 years.
• Roughly 94% of day traders lose money over time.
• Recessions are officially declared 6 to 12 months after they begin. The S&P 500 bottomed in March 2009.
• Rule of 72: at 10% a year, money doubles roughly every 7.2 years.

3. Verified at build time (2026-09-04), with sources

• S&P 500 "lost decade": annualized total return of about -0.9% to -1% from the end of 1999 to the end of 2009, dividends included. Sources: AMG Wealth, A Wealth of Common Sense.
• S&P 500 fell 56.8% (about 57%) from its October 9, 2007 close to its March 9, 2009 close. Sources: Federal Reserve History, Investment Company Institute.
• FDIC coverage: $250,000 per depositor, per insured bank, per ownership category. Source: FDIC.
• Free credit reports every week, permanently, at AnnualCreditReport.com. Source: FTC consumer alert, Oct 2023.
• Job changers' pay grew faster than job stayers' throughout 2026 (for example base pay +4.7% vs +3.0% year over year in August 2026). Source: ADP Pay Insights.
• Roth IRA: earnings are tax-free only as a qualified distribution, which requires five tax years since the first contribution and a qualifying event such as age 59½. Contributions can be withdrawn any time. Source: IRS Publication 590-B.
• Auto liability: many states' minimums are 25/50/25; the Insurance Information Institute recommends at least 100/300 for bodily injury. Sources: Insurance.com, CarInsurance.com.
• Renters insurance typically runs about $15 to $25 a month nationally. Sources: Insurance Information Institute via MoneyGeek, SoFi.
• Term life rule of thumb of 10 to 12 times income (some sources say 10 to 15). Sources: NerdWallet, Policygenius.
• Umbrella policy: $1 million of coverage typically costs a few hundred dollars a year (sources range from about $200 to $500), and insurers require minimum underlying auto and home liability limits first. Sources: NerdWallet, Progressive, Allstate.

3b. Fund descriptions (day 5)

• VOO is the Vanguard S&P 500 ETF and tracks the S&P 500 index. Source: Vanguard.
• QQQ is the Invesco QQQ Trust and tracks the Nasdaq-100, the 100 largest non-financial companies listed on the Nasdaq. Source: Invesco.
• SGOV is the iShares 0-3 Month Treasury Bond ETF and holds US Treasury bills with three months or less to maturity; it pays distributions monthly. Source: iShares.
• The Nasdaq-100 fell about 76% from its March 2000 peak to its October 2002 low and did not regain the 2000 peak until 2013 (already in the fact bank as the 2000 crash).
• The 40 / 40 / 20 split is the author's own starting allocation, labeled in the text as a starting point and not personal advice.

3c. Market facts (day 5)

• S&P 500 price-to-earnings ratio since 1871 (Shiller data): mean 16.23, median 15.08, read 2026-09-05. Source: multpl.com. The text rounds these to "about 16" and "near 15".
• Alan Greenspan's "irrational exuberance" remark was made on December 5, 1996; the S&P 500 and Nasdaq-100 peaked in March 2000 (the 2000 crash in the fact bank). Source: Federal Reserve, speech text.
• In 2022 the Federal Reserve raised its target rate from near zero to 4.25% to 4.50% within the calendar year, widely described as the fastest tightening since the early 1980s; the S&P 500 fell about 18% that year (fact bank). Source: Federal Reserve, open market operations history. The text says "the fastest pace in decades" and does not quote the rate levels.
• Earnings yield = 1 / P/E is arithmetic, computed in content/math.ts.
• Over 15 years, 89.5% of actively managed large-cap U.S. equity funds underperformed the S&P 500 (the text says "roughly 9 in 10"). Source: SPIVA U.S. Scorecard, S&P Dow Jones Indices, Mid-Year 2025, via InvestmentNews.
• The 1% fee chart is hypothetical: $300 a month for 30 years at 10% a year versus 9% a year, computed in content/math.ts (F.fee).

4. Clearly hypothetical

Introduced with "say" or "a made-up example": the $4,000 take-home month, the $3,200 month of needs, the $5,000 card at 24%, the 4% match on $50,000, the $700 car payment, the $300 of side income or half a raise, the $60,000 salary in the car rule, the $20,000 account that drops 30%, the $60,000 saver and $150,000 spender.

Also hypothetical, added with the charts: $300 a month started at 25 versus 26, 30, or 35 (the cost of waiting); a $300 raise every five years with half of it ($150) added to the transfer; the $5,000 card paid at $150 or $300 a month, year by year; a $4,000 payday split the 50/30/20 way with a $167 match; the cushion filled at $100, $200, $400, or $800 a month.

Rules of thumb (labeled as such in the text)

50/30/20 budget split, 15% of gross pay toward retirement, expense ratio thresholds, 20/4/10 car rule, "buy it twice" for wants, 5 to 7 years before buying a home, 20% down, three months of expenses (six if income swings), one month cushion first.

Deliberately left out because they change

Contribution limits, current savings rates, federal student loan program rules, balance transfer fee percentages, state-by-state insurance minimums. The guide tells the reader to check the current figure at the source.