In: Statistics and Probability
Your employer is going to invest $75 per month in a 401k for you and promised to average a 5% return over the next 20 years. What would I type into Excel to estimate how much money should be in the 401k after 20 years?
We first compute the equivalent number of months for 20 years here as: 20*12 = 240 months.
Therefore we need to compute the Future value of 240 installments here as:

After this we simply extend the formula for all the rows here and get the FV of each of the installment to get here:
| Month | Installment | Future Value |
| 1 | 75 | 198.997328 |
| 2 | 75 | 198.189878 |
| 3 | 75 | 197.385704 |
| 4 | 75 | 196.584793 |
| 5 | 75 | 195.787132 |
| 6 | 75 | 194.992708 |
| 7 | 75 | 194.201507 |
| 8 | 75 | 193.413516 |
| 9 | 75 | 192.628723 |
| 10 | 75 | 191.847114 |
| 11 | 75 | 191.068677 |
| 12 | 75 | 190.293398 |
| 13 | 75 | 189.521265 |
| 14 | 75 | 188.752265 |
| 15 | 75 | 187.986385 |
| 16 | 75 | 187.223613 |
| 17 | 75 | 186.463935 |
| 18 | 75 | 185.707341 |
| 19 | 75 | 184.953816 |
| 20 | 75 | 184.203349 |
| 21 | 75 | 183.455927 |
| 22 | 75 | 182.711537 |
| 23 | 75 | 181.970168 |
| 24 | 75 | 181.231807 |
| 25 | 75 | 180.496443 |
| 26 | 75 | 179.764061 |
| 27 | 75 | 179.034652 |
| 28 | 75 | 178.308202 |
| 29 | 75 | 177.5847 |
| 30 | 75 | 176.864134 |
| 31 | 75 | 176.146491 |
| 32 | 75 | 175.431761 |
| 33 | 75 | 174.71993 |
| 34 | 75 | 174.010988 |
| 35 | 75 | 173.304922 |
| 36 | 75 | 172.601721 |
| 37 | 75 | 171.901374 |
| 38 | 75 | 171.203868 |
| 39 | 75 | 170.509193 |
| 40 | 75 | 169.817336 |
| 41 | 75 | 169.128286 |
| 42 | 75 | 168.442032 |
| 43 | 75 | 167.758563 |
| 44 | 75 | 167.077867 |
| 45 | 75 | 166.399933 |
| 46 | 75 | 165.72475 |
| 47 | 75 | 165.052307 |
| 48 | 75 | 164.382592 |
| 49 | 75 | 163.715594 |
| 50 | 75 | 163.051303 |
| 51 | 75 | 162.389707 |
| 52 | 75 | 161.730796 |
| 53 | 75 | 161.074558 |
| 54 | 75 | 160.420983 |
| 55 | 75 | 159.77006 |
| 56 | 75 | 159.121778 |
| 57 | 75 | 158.476127 |
| 58 | 75 | 157.833096 |
| 59 | 75 | 157.192673 |
| 60 | 75 | 156.554849 |
| 61 | 75 | 155.919613 |
| 62 | 75 | 155.286955 |
| 63 | 75 | 154.656864 |
| 64 | 75 | 154.029329 |
| 65 | 75 | 153.404341 |
| 66 | 75 | 152.781889 |
| 67 | 75 | 152.161962 |
| 68 | 75 | 151.544551 |
| 69 | 75 | 150.929645 |
| 70 | 75 | 150.317234 |
| 71 | 75 | 149.707308 |
| 72 | 75 | 149.099856 |
| 73 | 75 | 148.49487 |
| 74 | 75 | 147.892338 |
| 75 | 75 | 147.292251 |
| 76 | 75 | 146.694599 |
| 77 | 75 | 146.099373 |
| 78 | 75 | 145.506561 |
| 79 | 75 | 144.916154 |
| 80 | 75 | 144.328144 |
| 81 | 75 | 143.742519 |
| 82 | 75 | 143.15927 |
| 83 | 75 | 142.578388 |
| 84 | 75 | 141.999863 |
| 85 | 75 | 141.423686 |
| 86 | 75 | 140.849846 |
| 87 | 75 | 140.278335 |
| 88 | 75 | 139.709142 |
| 89 | 75 | 139.14226 |
| 90 | 75 | 138.577677 |
| 91 | 75 | 138.015385 |
| 92 | 75 | 137.455375 |
| 93 | 75 | 136.897637 |
| 94 | 75 | 136.342162 |
| 95 | 75 | 135.788941 |
| 96 | 75 | 135.237965 |
| 97 | 75 | 134.689224 |
| 98 | 75 | 134.14271 |
| 99 | 75 | 133.598414 |
| 100 | 75 | 133.056326 |
| 101 | 75 | 132.516438 |
| 102 | 75 | 131.97874 |
| 103 | 75 | 131.443224 |
| 104 | 75 | 130.909881 |
| 105 | 75 | 130.378702 |
| 106 | 75 | 129.849678 |
| 107 | 75 | 129.322801 |
| 108 | 75 | 128.798062 |
| 109 | 75 | 128.275452 |
| 110 | 75 | 127.754962 |
| 111 | 75 | 127.236585 |
| 112 | 75 | 126.720311 |
| 113 | 75 | 126.206131 |
| 114 | 75 | 125.694038 |
| 115 | 75 | 125.184023 |
| 116 | 75 | 124.676077 |
| 117 | 75 | 124.170192 |
| 118 | 75 | 123.66636 |
| 119 | 75 | 123.164573 |
| 120 | 75 | 122.664821 |
| 121 | 75 | 122.167097 |
| 122 | 75 | 121.671393 |
| 123 | 75 | 121.1777 |
| 124 | 75 | 120.68601 |
| 125 | 75 | 120.196315 |
| 126 | 75 | 119.708608 |
| 127 | 75 | 119.222879 |
| 128 | 75 | 118.739121 |
| 129 | 75 | 118.257326 |
| 130 | 75 | 117.777486 |
| 131 | 75 | 117.299593 |
| 132 | 75 | 116.823639 |
| 133 | 75 | 116.349616 |
| 134 | 75 | 115.877517 |
| 135 | 75 | 115.407333 |
| 136 | 75 | 114.939057 |
| 137 | 75 | 114.472681 |
| 138 | 75 | 114.008198 |
| 139 | 75 | 113.545599 |
| 140 | 75 | 113.084877 |
| 141 | 75 | 112.626025 |
| 142 | 75 | 112.169034 |
| 143 | 75 | 111.713898 |
| 144 | 75 | 111.260609 |
| 145 | 75 | 110.809158 |
| 146 | 75 | 110.35954 |
| 147 | 75 | 109.911746 |
| 148 | 75 | 109.465769 |
| 149 | 75 | 109.021601 |
| 150 | 75 | 108.579236 |
| 151 | 75 | 108.138666 |
| 152 | 75 | 107.699883 |
| 153 | 75 | 107.262881 |
| 154 | 75 | 106.827652 |
| 155 | 75 | 106.394189 |
| 156 | 75 | 105.962484 |
| 157 | 75 | 105.532532 |
| 158 | 75 | 105.104324 |
| 159 | 75 | 104.677853 |
| 160 | 75 | 104.253113 |
| 161 | 75 | 103.830096 |
| 162 | 75 | 103.408796 |
| 163 | 75 | 102.989205 |
| 164 | 75 | 102.571317 |
| 165 | 75 | 102.155125 |
| 166 | 75 | 101.740621 |
| 167 | 75 | 101.327799 |
| 168 | 75 | 100.916652 |
| 169 | 75 | 100.507173 |
| 170 | 75 | 100.099356 |
| 171 | 75 | 99.6931935 |
| 172 | 75 | 99.2886791 |
| 173 | 75 | 98.8858061 |
| 174 | 75 | 98.4845678 |
| 175 | 75 | 98.0849575 |
| 176 | 75 | 97.6869687 |
| 177 | 75 | 97.2905948 |
| 178 | 75 | 96.8958292 |
| 179 | 75 | 96.5026654 |
| 180 | 75 | 96.1110969 |
| 181 | 75 | 95.7211172 |
| 182 | 75 | 95.3327199 |
| 183 | 75 | 94.9458985 |
| 184 | 75 | 94.5606468 |
| 185 | 75 | 94.1769582 |
| 186 | 75 | 93.7948264 |
| 187 | 75 | 93.4142452 |
| 188 | 75 | 93.0352083 |
| 189 | 75 | 92.6577093 |
| 190 | 75 | 92.2817421 |
| 191 | 75 | 91.9073004 |
| 192 | 75 | 91.534378 |
| 193 | 75 | 91.1629688 |
| 194 | 75 | 90.7930666 |
| 195 | 75 | 90.4246653 |
| 196 | 75 | 90.0577588 |
| 197 | 75 | 89.6923411 |
| 198 | 75 | 89.3284061 |
| 199 | 75 | 88.9659479 |
| 200 | 75 | 88.6049603 |
| 201 | 75 | 88.2454374 |
| 202 | 75 | 87.8873734 |
| 203 | 75 | 87.5307622 |
| 204 | 75 | 87.1755981 |
| 205 | 75 | 86.821875 |
| 206 | 75 | 86.4695872 |
| 207 | 75 | 86.1187288 |
| 208 | 75 | 85.7692941 |
| 209 | 75 | 85.4212773 |
| 210 | 75 | 85.0746725 |
| 211 | 75 | 84.7294741 |
| 212 | 75 | 84.3856765 |
| 213 | 75 | 84.0432738 |
| 214 | 75 | 83.7022604 |
| 215 | 75 | 83.3626307 |
| 216 | 75 | 83.0243791 |
| 217 | 75 | 82.6875 |
| 218 | 75 | 82.3519878 |
| 219 | 75 | 82.017837 |
| 220 | 75 | 81.685042 |
| 221 | 75 | 81.3535974 |
| 222 | 75 | 81.0234976 |
| 223 | 75 | 80.6947373 |
| 224 | 75 | 80.3673109 |
| 225 | 75 | 80.0412131 |
| 226 | 75 | 79.7164385 |
| 227 | 75 | 79.3929816 |
| 228 | 75 | 79.0708372 |
| 229 | 75 | 78.75 |
| 230 | 75 | 78.4304646 |
| 231 | 75 | 78.1122257 |
| 232 | 75 | 77.7952781 |
| 233 | 75 | 77.4796166 |
| 234 | 75 | 77.1652358 |
| 235 | 75 | 76.8521307 |
| 236 | 75 | 76.5402961 |
| 237 | 75 | 76.2297268 |
| 238 | 75 | 75.9204176 |
| 239 | 75 | 75.6123635 |
| 240 | 75 | 75.3055593 |
The future value finally is computed by adding the last column here to get:
FV =
| 30559.3337 |
Therefore at the end of 20 years, the account would have: $30,559