There is a rule you can do in your head, taught in personal finance for decades: divide 72 by a rate and you get roughly how many years that thing takes to double. Almost everybody learns it pointing at their savings. Point it at a debt and it explains something uncomfortable in about four seconds. Move the numbers below and watch it happen.
Everything on this page comes out of these two numbers. Not the size of the debt — the speeds.
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Nothing here is a prediction. These are your inputs; the page just does the arithmetic faster than you can. Only two numbers are fixed, and both are measured — see the bottom of the page for where they came from.
For scale: total federal revenue runs around $5 trillion a year, so “save $1 trillion” means setting aside roughly a fifth of everything that comes in, every year, forever, on top of running the government.
The long-run stock market average is often quoted near 10% before inflation. Treasury bonds are far lower. Pick whatever you think is honest.
7.5% is not a guess. It is what the debt actually did between 2016 and 2026, measured from Treasury’s own published record. Drag it to 0 to pretend the debt stops growing today.
| Saved per year | Earning | Debt growing | Caught in |
|---|
Every row is the same arithmetic this page runs on your sliders — nothing else changes.
Take any growth rate. Divide 72 by it. That is roughly how many years the thing takes to double. At 8%, money doubles about every 9 years. At 12%, about every 6. It is close enough to exact that people have been doing it on napkins for a very long time, and it needs no calculator, which is the entire point of it.
“It is not the amount. It is the rate against the other rate.”
Most people meet this rule from the friendly side — how fast their savings grow. The uncomfortable half is that anything growing does it too. A debt compounding at 7.5% doubles every 9.6 years whether anyone is watching or not. If your money grows slower than that, you are not gaining on it. You are falling behind while your balance goes up, which is the most confusing way to lose a race.
That is why the sliders above can put you in a place where saving a trillion dollars a year, forever, at a good return still never arrives. The number is not too big. The gap between the two rates is the wrong way round.
This is a simulator, not a forecast. Every scenario it produces is one you typed in. We are not predicting the debt, recommending a savings rate, or claiming any of this will happen. Change one slider and the answer changes completely — that is the feature.
It is deliberately simplified. Real public finance has inflation, interest paid on the debt itself, tax receipts that move with the economy, and a growth rate that does not sit still. None of that is modelled here. This is the napkin version, and the napkin version is enough to show the one thing it is for.
Two numbers are measured, and only two: the debt as Treasury last published it, and what it actually grew over the last decade. Both are linked below. Everything else on this page is a dial you turned.
Nobody is blamed here. This page names no party and no official. A compounding rate does not care who is in office, which is exactly why it is worth understanding before anyone tells you whose fault it is.
$40,102,964,278,586.10 — total public debt outstanding as published for September 3, 2026 by the U.S. Treasury, Debt to the Penny.
7.50% a year — measured, not assumed. The same Treasury dataset shows $19,482,694,389,006.50 on September 9, 2016 and $40,102,964,278,586.10 on September 3, 2026. Over 9.98 years that is a compound rate of 7.50%.
The live figure, updated daily from that same source, is on the front page, and you can put it on your own site from the widget page.
A rule that fits on a napkin, pointed at a number that does not. Nothing on this page is stored, sent, or tracked — the arithmetic runs entirely in your own browser.
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