The objectives of this study were to compare measurements of retention and prececal (pc) digestibility in evaluating mineral phosphorus (P) sources in 3- and 5-wk-old broilers. A corn-soybean meal-based basal diet was used (0.35% P on DM basis). Anhydrous monosodium phosphate (MSP(a)) or anhydrous dibasic calcium phosphate (DCP(a)) was supplemented to increment the P concentration by 0.08%, 0.16%, and 0.24%. Titanium dioxide was used as the indigestible marker. Two retention trials with excreta collection from d 16 to 20 and d 30 to 34 were conducted (n = 8 birds per diet). Another 8 pens of 10 birds from the same hatch were allocated to each diet on d 11 or 25 each to measure pc digestibility in both age periods. After 10 d of feeding, these birds were euthanized and the content of a defined section of the terminal ileum was obtained. Percentage P retention and pc digestibility for MSP(a) and DCP(a) were calculated by linear regression analysis. In 3-wk-old broilers, P retention for MSP(a) was 70% and significantly higher (P < 0.001) than for DCP(a) (29%). Values determined for pc digestibility at the same age were very similar (67% for MSP(a) and 30% for DCP(a); P < 0.001). In 5-wk-old broilers, P retention was 63% (MSP(a)) and 29% (DCP(a); P < 0.001) and pc digestibility was 54% (MSP(a)) and 25% (DCP(a); P = 0.002). We concluded that both retention and pc digestibility can be used for evaluating mineral P sources in broilers based on a regression approach. In 3-wk-old broilers, results obtained with both approaches were the same. In 5-wk-old broilers, the ranking of the 2 P sources was also the same for both approaches. Values did not differ significantly between the 2 age periods, but further studies on the relevance of broilers' age in P evaluation are suggested.