When size changes the answer: ten dollars, ten thousand, and a hundred million are not the same money

Why the calculator is right and the answer is wrong

Every tool on this site does honest arithmetic, and arithmetic scales in a straight line: double the money, double the result. For most people at most sizes that is the truth. But the world has lines drawn across it, and when a sum crosses one, the same act becomes a different act. A thousand dollars and a million dollars in a CD have the same interest rate and completely different safety. Ten dollars and a hundred million dollars in a stock have the same expected return and completely different reality. This page is about the lines, so that when a number on a calculator crosses one, you know the calculator has stopped telling the whole story.

Cash: where the insurance ends

Bank deposits are insured by the FDIC, and credit union deposits by the NCUA, up to a limit per depositor, per bank, per ownership category. The limit is a fixed number the law sets; the FDIC page linked below states it. A thousand dollars in a CD is fully covered. A million dollars in one CD at one bank is covered up to the limit and, above it, is an unsecured loan to that bank. Larger sums stay insured by being spread: several banks, brokered CDs through one brokerage that places money across many banks, ownership categories that each carry their own limit, or Treasury bills, which are backed by the government with no limit at all and often pay as much as a CD. This is why the ladder tool notes the line when a rung crosses it. The rate did not change. The guarantee did.

Stocks: where your order becomes the market

A stock's price is set by the last trade, and a small order is a drop in that river. Ten dollars, a thousand, even a hundred thousand in a large company trades at the quoted price with no effect. As the order grows toward a meaningful fraction of what trades in a day, it starts to move the price against itself: buying pushes the price up before the order fills, selling pushes it down. Traders call it impact, and it is a real cost that never appears on a fee schedule. A hundred million in a large company is a few days of careful trading; a hundred million in a small company may be more than the stock trades in months, which means it cannot be sold at anything like the quoted price and may not be sellable at all without moving the price by a large fraction. Ownership also crosses regulatory lines: past certain percentages of a company, the owner must file public reports, may be treated as an insider with restrictions on selling, and in some cases must announce intentions. Size turns an investment into a relationship with the company and the regulator.

Funds and bonds: where size buys a discount

Here size works in the other direction. Many funds have cheaper share classes above a minimum, and institutional pricing on the same portfolio for larger sums. Bonds trade with a spread that narrows for round lots, so small bond purchases pay more than large ones for the same paper, which is one reason bond funds exist. Advisers charge a percent that steps down as assets grow. Brokerages offer things at ten million they do not offer at ten thousand: securities based lending at low rates, direct indexing, access to funds that require a minimum investment or accredited status, which is itself a size line the law draws. The person with more pays less per dollar, which is one of the quiet ways wealth compounds faster than income.

Taxes and benefits: where lines are drawn in income

The tax code is a staircase of lines. Below one, a credit pays you. Above another, a deduction phases out. Above the next, a surtax appears. Above a higher one, the estate tax applies to what is left at death. Every one of these is a size line, drawn in income or in wealth, and the guide on money at every level walks them rung by rung. What matters here is the shape: the same additional thousand dollars is worth a different amount on each side of each line, and a person planning a raise, a bonus, a sale, or a withdrawal is planning where they land on the staircase, not just how much they get.

Your own wealth: the only line that is yours

The lines above are drawn by insurers, markets, and the law. One line is drawn by you: what share of your own wealth a single thing represents. Ten dollars in a stock is nothing to anyone. Ten thousand in one stock is a fifth of someone's savings and a rounding error for someone else. A hundred million in one stock is a fortune and, for the person who founded the company, may be nearly all of one. The habitat page shows this fraction and calls it concentration. No calculator can tell you what a sum means without knowing what it is a fraction of, which is why every tool here asks for the whole picture and why the founding page says the fraction is the whole of it.

A worked example

Three people each put money in a one year CD paying 4.5 percent at one bank. The first puts in $1,000 and earns $45, fully insured. The second puts in $1,000,000 and earns $45,000, insured up to the limit and exposed above it; the same million spread across five banks, or in Treasury bills, earns about the same and is exposed to nothing. The third puts in $100,000,000 and finds that no single CD makes sense at all: a ladder of Treasury bills, a money market fund, or a bank's institutional desk is how sums of that size hold cash, and the 4.5 percent is now a negotiation. Same product, three different worlds, one calculator.

Questions to answer before you leave this page

For any cash you hold, is all of it under an insurance limit, at each bank, in each ownership category? For any stock you hold, what fraction of a day's trading would selling it be, and could you leave in a week? For any sum you are about to add or remove, which income line does it cross, and what changes on the other side? What minimum or discount would this sum qualify for that a smaller one would not? And what fraction of everything you hold is this one thing?