The objective of this study was to define the nitrogen retention (NR) response of growing dairy calves as a function of dietary lysine intake (DLI) and body weight (BW). Raw, individual calf data from 3 published papers were collected. Lysine intake and NR were expressed as g per kg BW. Twelve models were derived relating NR, DLI and BW. Three equation forms (logistic, Michaelis-Menten or exponential), 2 effect types (fixed effects or mixed-effects with random study effect) and 2 error assumptions (equal error variance or heterogeneous error variance) were considered. The models were evaluated and compared based on their root mean squared prediction error (RMSPE), concordance correlation coefficient (CCC) and any mean and slope bias revealed by residual analysis. The asymptotic and rate-determining parameters of each function were assumed to vary as a function of BW and the primary explanatory variable within each equation form was DLI. Models varied notably in their predictive capacity and RMSPE ranged from 14.4 to 58.9%. A fixed-effects, logistic model with equal error variance returned the lowest RMSPE (14.4%), highest CCC (0.94) and had no appreciable mean or slope bias. All parameters were statistically significant (P < 0.01). This equation, NR = (0.89–0.0067 × BW+0.000015 × BW2) ÷ (1+e(-((Lys-(0.0024 × BW*e(−0.013 × BW)))/0.032))), estimated that a young calf (50 kg BW) could potentially achieve a maximal NR efficiency of 2.72 g/g DLI/kg BW and at 250 kg BW a maximal NR efficiency of 1.25 g/g DLI/kg BW could be reached. Nitrogen retention efficiency reduced substantially as BW increased. Increasing DLI promoted NR at low BW more effectively than at high BW. Although DLI affects short-term protein accretion responses, NR rate was primarily dependent on calf maturity.