A few FI ideas that survive contact with a calculator

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.