Every year around this time Calcbench examines the effect of exchange rates on corporate cash.

Why? Because the value of the dollar has important effects on cash. For example, a weaker U.S. dollar means purchasing foreign supplies becomes more expensive, potentially driving up your cost of goods sold. At the same time, selling overseas goods also becomes less expensive, because overseas customers have more purchasing power. During periods of a stronger dollar, that situation is reversed.

Companies must track the effect of exchange rates on cash in a line-item on the Statement of Cash Flows, unglamorously called “Effect of Exchange Rate on Cash.”

So Calcbench examined the amount of cash and equivalents that the S&P 500 reported at the end of 2017, and looked to see how much the exchange rate pushed that sum upward or downward.

First, how did the U.S. dollar do in 2017, anyway?

According to the Federal Reserve of St. Louis, not too good. The dollar began 2017 worth roughly 94.6 cents against a basket of major currencies, reached a low point of 86 cents in September 2017, and closed out the year at 87.4 cents. Take a look.

That said, the dollar is still up markedly from earlier in the decade. It bounced around 75 to 80 cents in the early 2010s, before inexorably rising as the Fed began raising interest rates in the mid-2010s.

Long story short: as the Fed raised rates in the mid-2010s, the dollar got stronger, so the exchange rate started to chew into cash and equivalents. Here are the numbers for 2012 through 2017.

What happened in 2016? The dollar stopped rising. It started the year at 95 cents, drifted downward to 90 cents, and ended 2016 right around 95 cents again. Hence the exchange rate effect decelerated to nibble at cash rather than chew.

And as the dollar continued to slide against other currencies in 2017 — mostly due to other economies finally reviving, and their currencies strengthening relative to ours — the exchange rate effect actually turned positive. It boosted the value of cash among the S&P 500 by 1.5 percent.

We know what you’re thinking: cool story bro, but what about 2018?

So far, the St. Louis Fed says, the dollar has trended largely downward: from 96.4 cents in January to 89.5 cents as of this week. That may be because of the mushrooming U.S. debt (which puts a lotta dollars out there), or stronger economies elsewhere, or a mix of both.

Regardless, if past is prologue, that means cash levels will get a little extra oomph again early next spring thanks to exchange rates.