Warner received 500 hours of community service and two years probation in January after pleading guilty in October to using a Swiss bank account to evade millions of dollars in taxes.
He also had to pay $27 million in back taxes and interest, and $53.6 million in penalties.
Sentencing guidelines recommended 46 to 57 months of prison time for the crime, and prosecutors argued for at least a year in jail.
At the time of sentencing, U.S. District Judge Charles Kocoras said Warner's time would be better served out of jail so the billionaire could continue to do charitable work.
Prosecutors argued that others convicted of the same crime for smaller amounts of money got prison time. They also said Warner's embarrassment of prison time shouldn't be taken into consideration.