Mid-ocean ridge transform faults (RTFs) have thermal structures that vary systematically with tectonic parameters, resulting in predictable seismic characteristics and clear seismic cycles. We develop a scaling relation for repeat time, t_R, of the largest expected earthquake, M_C: t_R = μ⁻¹Δσ^2/3C_Mc^1/3A_T^1/4V⁻¹, where μ is the shear modulus, Δσ is the stress drop, C_Mc is a constant, A_T is the area above 600°C, and V is the slip rate. We identify repeating M_C earthquakes by measuring differential arrival times of first orbit Rayleigh waves to determine centroid offsets between pairs of events. Comparing our observations of t_R (5–14 years for earthquakes on Gofar and Blanco RTFs) with predictions from our scaling relation, we can constrain RTF stress drops. Specific tests of this scaling relation are proposed for earthquakes on Blanco, Gofar, Discovery, and Clipperton RTFs, which are all expected to have large ruptures in the next few years.