FTX founder Sam Bankman-Fried was sentenced Thursday to 25 years in prison for his role in the fraud and conspiracy scandal that took place at the crypto exchange. That was far less than the 40 to 50 years prosecutors were lobbying for, but about five times the sentence his own lawyer had requested.

But will Bankman-Fried serve all that time? Almost certainly not. His lawyers plan to appeal the conviction and the sentence. However, if that fails, legal experts say that while SBF will see his sentence reduced, it won’t be by the drastic amount some felons receive for good behavior.

Christopher Zoukis, a federal prison consultant based out of Charleston, South Carolina, estimates SBF will likely serve about three-quarters of the sentence.

Here’s how the math works. First, SBF will also be credited for the time he spent in prison before Thursday’s hearing, shaving 7.5 months or so off his remaining time in incarceration.

Next, like all federal prisoners, SBF will automatically get a 15% reduction in his sentence for good conduct, reducing it by 45 months. That’s applied preemptively, usually within the first couple weeks of being in custody, says Zoukis.

“If he gets into serious trouble after that, that can be taken away, but that usually doesn’t happen,” Zoukis told Fast Company.

From there, there are a couple other steps SBF can take to cut down his time in jail. In his first 28 days in prison, he will go to what’s called a classification meeting for the First Step Act, a criminal justice reform bill signed into law in 2018 that aims to reduce the federal prison population and reduce recidivism.

Through that act, he’ll be able to accrue Earned Time Credits (ETC), which can be used to reduce the amount of time spent in secure custody/prison. The first year he’s in prison, he can earn 10 days for every month he’s in the program (cutting the sentence by up to 120 days). In year two, that earning can go up to 15 days for every month. All totaled, ETC can shave about a year off his sentence.

If SBF had an alcohol or drug abuse problem, joining a treatment program could reduce his sentence a bit more, but that’s unlikely. Pretrial, he pushed back against allegations of rampant drug use at FTX.

“I had maybe half a glass of alcohol a year, roughly speaking,” he told Andrew Ross Sorkin at the New York Times Dealbook conference in late 2022. “There were no wild parties here. When we had parties, we would play board games. . . . I can say for me, I have been prescribed various things at various times to help with focus and concentration, and I think they have done that. . . . I think these have totally been on-label use of medication.”

At the backend of his sentence, SBF will be eligible for entering a halfway house, where he can leave for work, medical appointments, and typically a brief social pass each week. Prisoners are eligible for a full year in a halfway house, but “the likelihood of getting 12 months is slim,” said Zoukis. “I would assume nine months is a more likely amount.”

And, assuming he is a model prisoner, SBF could spend the last six months of his sentence in home confinement.

Add it all up, including the presentencing incarceration and halfway house/home confinement, and SBF could finish his sentence in about 18.5 years—putting him back on the street in the fall of 2042.

This is, of course, a broad estimate—and things could change over time. But even Bernie Madoff attorney, Ira Sorkin, says SBF should get comfortable in jail.

“He will not have to serve the full 25 years,” Sorkin told CNBC Thursday. “He will have the opportunity to get out sooner, but certainly he’ll have to spend a good portion of that 25 years in prison.”