For loans with a maturity of 179 months or less, there are no prepayment penalties

For loans with a maturity of 180 months or longer, prepayment penalties apply when:
The borrower voluntarily prepays 25 percent or more of the outstanding balance of the loan.
The prepayment is made within the first three years after the date of the first disbursement of the loan proceeds.

The prepayment fee is as follows:
During the first year after disbursement, 5 percent of the amount of the prepayment.
During the second year after disbursement, 3 percent of the amount of the prepayment.
During the third year after disbursement, 1 percent of the amount of the prepayment.

*Source: sba.gov