This can be calculated in any one of a number of "on-line" calculators, either at the Social Security website or at other sites (maybe even AARP has one).
The best calculator is that published by the Social Security Administration and is run on your own computer. However, it can be a bit tricky to learn how to use and run. This is the "Anypia32" software.
I ran the scenario you outlined, working 50 years and making $50,000 every one of those years. I set the program (Anypia32) to have this person born in 1948, worked 50 years from 1968 through 2017, inclusive, earning $50,000 each one of those years. Of course, this is not a very realistic example as wages would likely have gone up with inflation. Even someone who "topped out" in their pay grade at $50,000 their first year of work would likely see some increases along the way.
So the benefit for this person at age 70 retirement would be $3,255 per month (single)
But, y'know, this is not the "maximum" case. There is a ceiling each year above which earnings are not subjected to payroll SS tax. For this guy in our example, his $50,000 would have been way above the ceiling for a number of years at the beginning. Then inflation would have caught up and he would be below the ceiling. Consequently, he will not get the maximum SS benefit.
Someone who did earn at least the ceiling amount every year (for the 35 highest years considered by the SS) their benefit would be $3,698
(Disclaimer: I am not a SS expert, they will be along shortly. I ran using Anypia32 version 2019.1. The guy was born in 1948 (January 31), started working in 1968 at age 20, worked 50 years (through 2017), then retired and collected benefits at age 70 in 2018. I spent about 20 minutes working on this, maybe 30, so I don't have this especially refined so the results may be somewhat coarse.)
