# A few FI ideas that survive contact with a calculator Savings rate, the first large milestone, doubling time, and why medians and averages tell different stories. ## The savings rate does most of the early work From a standing start, the share of income you do not spend decides both how much you invest and how little the portfolio must replace. At a 5% real return and a 4% withdrawal rate, this site's chart puts a 10% savings rate near 50 years and a 50% savings rate near 16 years. The return matters, and it is not the first lever. The full chart is on the compound-interest calculator. ## Doubling time The Rule of 72 divides 72 by the annual percent. At 7% the sketch says about 10.3 years to double a lump sum. The exact annual compound doubling time is log(2) / log(1.07), about 10.2 years. Close enough for a conversation. Not close enough to skip the calculator when contributions are involved, because contributions do not double on that schedule. They have their own shorter lives in the account. ## The first large chunk feels slow Early balances move mostly because you added money. Later balances move because the balance is large. Charlie Munger described the first $100,000 as the hard part, after which compounding does more of the lifting. The line is a motivation, not a threshold in the tax code. For some incomes $100,000 is a short project. For others it is a decade. The shape — contributions first, growth later — is the part that holds. ## Medians, means, and you The 2022 SCF mean net worth is over a million dollars. The median is $192,900. The mean is not a typical household. Comparing yourself with an average that includes billionaires produces a mood, not information. Use a median for context and your own spending for a target. Both tables are on the savings-by-age page. > These are orientation notes. The calculators are the part that uses your inputs. HTML: https://wealthcompounds.com/fi-insights --- Educational only. Not investment, tax, or financial advice. Canonical HTML: https://wealthcompounds.com