We developed a purely empirical model for the estimation of stability constants of acetate mono-complexes of four lanthanides (La3+, Nd3+, Gd3+, and Yb3+) at different ionic strengths (I=0.1–2.0molkg−1) and temperatures (t=25–70°C). The standard errors, S.E., were 0.09, 0.05, 0.06, and 0.07, for La3+, Nd3+, Gd3+, and Yb3+ complex, respectively. We also developed common model for the complexes of all metals studied (S.E.=0.11), which enables prediction of log K1 for a metal, at different conditions, knowing the value of its constant measured at only one ionic strength and temperature. ► We developed an empirical model for the estimation of K1 of lanthanide complexes. ► K1 of acetate complexes with La3+, Nd3+, Gd3+, and Yb3+ was modeled. ► Model allows simultaneous estimation of K1 of complexes of different metals. ► Model enables estimation of K1 at I=0.1–2.0molkg−1 and t=25–70°C.