Objective To compare serum insulin-like growth factor 1 (IGF-1) and peak growth hormone (GH) levels between girls with isolated premature thelarche (IPT) and central precocious puberty (CPP), to construct a prediction model for progression from IPT to CPP, and to assess its diagnostic value. Methods Girls diagnosed with IPT (n=111) between January 2022 and August 2023 at the China-Japan Friendship Hospital and the Xinjiang Production and Construction Corps Hospital were retrospectively included. According to follow-up outcomes, participants were categorized into a CPP group (35 cases) and an IPT group (36 cases). A clinical prediction model for progression to CPP was constructed by multivariable logistic regression, and the contributions of IGF-1 and peak GH were evaluated. Restricted cubic spline analysis was used to assess the dose-response relationships of IGF-1 and peak GH with CPP. Decision curve analysis was applied to evaluate clinical utility. Results IGF-1 and peak GH were higher in the CPP group than in the IPT group (P<0.05). Compared with model 1 (without IGF-1 and peak GH), model 2 (with IGF-1 and peak GH) showed significantly higher area under the curve, integrated discrimination improvement, and net reclassification improvement (all P<0.05). Model 2 ({\chi }^{\mathrm{2}}=6.054, P=0.889) also demonstrated better goodness-of-fit than model 1 ({\chi }^{\mathrm{2}}=7.717, P=0.634). Nonlinear dose-response relationships were observed for peak GH and IGF-1 with CPP (P for overall trend <0.05; P for nonlinearity <0.05). Decision curve analysis indicated that combined prediction using IGF-1 and peak GH provided greater net benefit than either biomarker alone. Conclusions Peak GH and IGF-1 are closely associated with progression from IPT to CPP in girls. A clinical prediction model incorporating peak GH and IGF-1 can improve prediction of progression to CPP and yield higher net benefit.