Wis. Stat. § 422.208: Right to prepay.

Subject to s. 422.209 and, with respect to a motor vehicle consumer lease, s. 429.207, the customer may prepay in full or in any part, at any time without penalty, the unpaid balance of any consumer credit transaction other than a transaction secured by a first lien mortgage or equivalent security interest on real estate with an original term of 10 years or more and on which the annual percentage rate disclosed pursuant to subch. III is 10 percent or less.