Selecting soybean (Glycine max (L.) Merr.) planting date and maturity group are important agronomic decisions that are often affected by unfavorable weather. The objective of this study was to quantify how the selection of maturity groups and later than optimal planting dates effected soybean seed yield and crop development over time across Iowa, US. Field experiments were conducted at seven locations between 2014 and 2016 for a total of 21 environments. Cultivar maturities varied by location (ranging from 2.2 to 2.5 MG) and planting dates were scheduled for 20-day intervals from early May to early July. Studied planting date and maturity group combinations that resulted in grain yields ranging from 0.27 to 7.54 Mg ha-1. Analyses showed that the main effect of maturity group had little (3.28 to 4.30 Mg ha -1) to no effect on grain yield at 4 of 7 sites while the main effect of planting date was significant (p < 0.001) at all sites. The interaction of planting date and cultivar maturity was not significance. With delayed planting dates, the length of the non-grain filling (VE-R3) and grain filling (R3-R7) period were shortened by up to 15-20 days, resulting in less radiation, smaller growing degree day accumulation, and lower yields. Across northern Iowa, there was a critical radiation accumulation of 946 MJ whereas the critical radiation accumulation (1074 MJ) was much higher across southern Iowa. These results show that yield potential would be maximized by planting before May 20 using a cultivar maturity group that is well-adapted to specific location or geography. To maximize yield, planting soybean earlier in the growing season was a better management practice than maturity selection, and the duration of the grain filling period was critical in determining potential yield each growing season.