Common wisdom has it that the last few days of any calendar year are the best time to buy a car.

Not only are franchised dealers and their salespeople seeking to close out the month with a bang, but it's the end of a year and their allocation of cars next year can depend on how many they sell this year.

In other words: bargains may be there for the taking.

DON'T MISS: Senate tax plan leaves electric-car purchase credit in place

But this year, there may be another reason to buy a plug-in electric car by December 31.

It's possible that the U.S. income-tax credit of $2,500 to $7,500 for buying a plug-in car may be ended if Congress manages to pass a "tax reform" bill.

Of the two drafts for a tax bill introduced in recent weeks, the one from the House of Representatives ended the credit as of the end of this year, but the Senate version didn't.

UPDATE: This article was published on December 1, 2017. The text of the final tax bill, following reconciliation of the individual bills passed by the House and the Senate, was released on December 15. The plug-in electric vehicle income-tax credit was not ended by that bill, so whatever happens when Congress votes on the bill, the tax credit will survive.

U.S. Capitol Building

U.S. Capitol Building

At this stage, it's impossible to know the fate of any tax bill, given rapidly changing news and the usual political horse-trading in D.C.

But if you'd intended to buy a battery-electric or plug-in hybrid car in the next few months, you might well be advised to consider moving your purchase up to this month.

READ THIS: House tax bill eliminates credit for all electric-car buyers: report

Regardless of what happens in Congress, the income-tax credit will remain available through the end of this year.

Not every buyer is necessarily eligible for the full tax credit; that depends on the individual tax return and, as always, you should consult a tax professional if necessary.

2017 Chevrolet Bolt EV

2017 Chevrolet Bolt EV

The income-tax credit is based on battery-pack size, with the lowest $2,500 credit applying to cars with 4 kilowatt-hours of capacity and the highest $7,500 to cars with 16 kwh or more.

That means some plug-in hybrids get a credit amount somewhere between the two, while every battery-electric vehicle qualifies for the maximum credit.

CHECK OUT: Ending tax credits would kill electric-car market, Edmunds says

State and local incentives, including California's purchase rebates and carpoool-lane access, will not be affected by any tax bill passed this year (or next) by Congress.

Meanwhile, if you're considering buying that electric car but just can't do it by December 31 ... keep your eye on the news from D.C.

[hat tip: John Briggs]


Follow GreenCarReports on Facebook and Twitter.