Electric-car sales skyrocketed in the U.S. last year as Tesla Model 3 production ramped up.

The growth came not only as Tesla's production blew through its allotment of federal tax credits, but also as changes based on the 2017 tax law raised many taxpayers' tax bills, come last month.

Anecdotally, we heard complaints from quite a few readers who bought electric cars (mainly Tesla Model 3s) in 2018 (before Tesla tax credits began winding down), who said most of the federal Plug-in Vehicle Tax Credits they earned were swallowed up in higher tax bills that came due last month.

READ THIS: If you bought an EV last year, how did it affect your tax bill? Take our Twitter poll

So we wondered how many electric car buyers were in that situation.

The Federal Electric Vehicle Tax credit is worth $7,500 for most electric cars, though it began to sunset on Teslas and Chevrolet Volts and Bolt EVs in 2019, because Tesla and GM have surpassed the threshold of 200,000 electric car sales that triggers the wind-down of the tax credits. Those 2019 sales are not what our poll addressed.

The tax credit is structured so that taxpayers can only claim up to the maximum amount of their tax bill. Many readers who bought EVs in 2018 expected a windfall when they filed their taxes in 2019—one that never materialized. 

Our Twitter poll last week asked: "If you bought an EV last year, how much tax credit did you earn?"

The choices included $7,500, the maximum amount; $5,000 to $7,500; $3,750 to $5,000; and less than $3,750.

It turned out, the readers who told us they got less than they expected were in the minority. The vast majority of respondents, 69 percent, said they received the full tax credit in their refund.

The next largest group, however, said they received less than $3,750: 17 percent.

CONSIDER THIS: Commentary: Overdue for reform, EV tax credit needs reasonable limits

Very few respondents wound up in the middle, with 9 percent saying they received more than $5,000 but less than $7,500, and only 5 percent receiving less than $5,000 but more than $3,750.

As always, our Twitter polls are unscientific, and in this case nothing to plan your taxes by. Our sample sizes are too small, and, as with those who contacted us about their tax bills, self-selected.

Still, if you're planning to buy an EV in 2019 and claim the credit, you might want to check in with your accountant or tax preparer—the sooner the better—to see how you can take the best advantage of it.