Here are the data for monthly stock price data for the S&P 100 index and calculate monthly return rates as the percent change in monthly adjusted closing prices.

High null Low Close Adi Close null Volume null Date 2017/12/1 2018/1/1 2018/2/1 2018/3/1 2018/4/1 2018/5/1 2018/6/1 2018/7/1 2018/8/1 2018/9/1 2018/10/1 2018/11/1 2018/12/1 2018/12/3 Open null 1187.32 1273.99 1187.32 1251.42 1251.420044 73366640000 1248.27 1258.88 1120.08 1201.87 1201.869995 79579410000 1202.46 1235.97 1131.98 1157.37 1157.369995 76349800000 1153.54 1192.22 1118.691160.73 1160.72998 1158.41 1206.85 1138.55 1188.911188.910034 75617280000 1194.91226.48 1182.93 1194.5 1188.68 1261.57 1185.61 1241.76 1241.76001 1246.28 1292.94 1236.41286.9 1286.90002469238220000 1284.52 1304.27 1267.62 1294.27 1294.27002 1300.38 1309.73 1159.55 1208.84 1208.839966 91327930000 1211.33 1253.12 1161.12 1225.19 1225.189941 80080110000 1240.01 1244.34 1231.92 1238.63 1238.630005 null null 69648590000 1194.5 77439710000 64542170000 62492080000 4186060000 0 0 0 0 1238.63 1238.630005