Let M and N be unital Jordan-Banach algebras, and let M −1 and N −1 denote the sets of invertible elements in M and N , respectively. Suppose that M ⊆ M −1 and N ⊆ N −1 are clopen subsets of M −1 and N −1 , respectively, which are closed for powers, inverses and products of the form Ua(b). In this paper we prove that for each surjective isometry ∆ : M → N there exists a surjective real-linear isometry T 0 : M → N and an element u 0 in the McCrimmon radical of N such that ∆(a) = T 0 (a) + u 0 for all a ∈ M.Assuming that M and N are unital JB * -algebras we establish that for each surjective isometry ∆ : M → N the element ∆(1) = u is a unitary element in N and there exist a central projection p ∈ M and a complex-linear Jordan * -isomorphism J from M onto the u * -homotopefor all a ∈ M. Under the additional hypothesis that there is a unitary element ω 0 in N satisfying Uω 0 (∆(1)) = 1, we show the existence of a central projection p ∈ M and a complex-linear Jordan * -isomorphism Φ from M onto N such that ∆(a) = U w * 0 (Φ(p • a) + Φ((1 − p) • a * )) , for all a ∈ M.