Can you pay off a buy here pay here car early?

Usually yes, and on a high-interest loan it's the single biggest saving available to you — but check for a prepayment penalty first, because some contracts have one and it changes the math.

Ask the lot for a written payoff quote rather than assuming it's the sum of your remaining payments. On most of these loans interest is calculated as you go, so paying early means you skip interest that hasn't accrued yet and the payoff is less than the payments left. On a precomputed-interest contract it works differently — the interest is baked in from day one, and paying early saves you much less than you'd expect.

Which kind you have is written in your contract, and the lot will tell you if you ask. It's worth knowing before you throw a tax refund at it.

One more thing to line up: when the balance hits zero, make sure the lot releases the title and removes any GPS or starter interrupt device. Ask for the lien release in writing. A paid-off car that still has the lot's hardware in it isn't finished.