Iowa Code § 668.7: Effect of release.

A release, covenant not to sue, or similar agreement entered into by a claimant and a person liable discharges that person from all liability for contribution, but it does not discharge any other persons liable upon the same claim unless it so provides. However, the claim of the releasing person against other persons is reduced by the amount of the released person’s equitable share of the obligation, as determined in section 668.3, subsection 4.