Want to see how you could have made 75 percent on your money in less than two years by buying a low-interest bond that looked so financially toxic when it was issued that it should have come with a warning sticker?

Welcome to the 100-year, 2.1 percent bond that the Austrian government sold in September of 2017.

Those two numbers describing the bond aren’t typos. The bond really does come due in 2117, a century after it was issued. And it carries a cheesy 2.1 percent interest rate, despite which buyers scarfed down 3.5 billion euros worth as if the Austrian treasury was offering them bargain-priced Bergkäse, the country’s famous mountain cheeses.

But you know what? When last I looked, the bond was trading at a bit over 170 percent of face value. Add the 4 percent or so that the bond’s owners have made in interest since it was issued, and people who bought the bond at face value in 2017 are up about 75 percent on their money. At least on paper.

And wait, there’s more. In late June, the Austrian government reopened the issue and sold another 1.25 billion euros worth at about 154 percent of face value. That’s an annual cash interest yield of about 1.4 percent for what had become a 98-year bond.

Looking at it another way, it would take almost 26 years of interest payments just to get back the premium over face value that speculators — I won’t call them investors — paid the Austrian government for the newly issued bonds.

Why am I inflicting all these numbers on you? Because they show what can happen when momentum madness strikes the financial markets. And the numbers help explain negative-interest madness in Europe and Japan, where rates keep falling deeper and deeper below zero.

When buyers keep bidding up bond prices, which pushes bond yields lower, it becomes a self-fulfilling cycle — regardless of the bonds’ fundamental values (or lack of them).

The bonds’ prices keep going up because they’re going up, which is how momentum investing — a.k.a. speculating — works.

Momentum madness also helps explain how bonds of an issuer like Greece — a financially distressed (to be polite) country borrowing euros, a currency that it can’t print — have yields comparable to those of equivalent U.S. Treasury securities. Which are dollar securities issued by the Treasury, which can print as many dollars as it needs to redeem its obligations.

Now, let me try to show you why I think these Austrian bonds are speculations rather than investments.

So far, pretty much everyone who’s disregarded what people like me told them (or would have told them) and bought the Austrian 2.1 of 2117 — the bond’s official description — is ahead. Way ahead. Even the purchasers of the recently issued additional bonds are up 16 points (about 10 percent) on their money in a mere month.

The fact that everyone who’s bought this security is ahead leads other players to buy. Which leads other players to buy. And so on and so on and so on.

But when the yield on this bond begins to rise, which is inevitable at some point between now and 2117, and the price begins to fall, you can bet there will be a stampede out of this security the same way there was a stampede into it.

And things could get really ugly really quickly.

Here’s the math, hot off a Bloomberg machine (which is where most of this column’s numbers come from). If the yield on these bonds rises half a point in a year, its price will fall to 132 from its current 170-plus. If the rate is up a whole point, the price will fall to 105. Those are big-time declines.

On the other hand, if the yield on these bonds is a half point lower in a year, it will trade at about 226. And if the yield falls by a point, the bond will trade for 309. Those are big-time increases over the current price.

Think about those numbers for a while, and you realize that these securities are more like gambling chips than bonds.

I don’t know who’s going to come out ahead from here by betting on these things, and who’s going to come out behind. But I can sure tell you who the biggest winners in this game are: the taxpayers of Austria. They’ve locked in cheap 100-year money and ultracheap 98-year money.

And that’s the bottom line.

Doris Burke of ProPublica and Alice Crites contributed reporting.