There are 27 million known infections in the US. 76 million would mean that you are estimating almost 3 times the number of known infections to calculate total infections. I've heard people say that the total number of infections is about 8 times higher than known infections.
Why do you estimate 76 million?
I find it’s more plausible to work backwards using the infection fatality rate (IFR) numbers. We have 461,930 confirmed dead, divided by the IFR of 0.65% gives us 71 million cases resolved (one way or another) plus those currently infected. To get that, take the ratio of cases diagnosed to actual cases (using the above IFR, giving you ~2.617), take the 7-day moving average for the past week, times two (mean time from diagnosis to death ~13 days), giving you another ~5.5 million actively infected without a case resolution.
Moving forward, that’s ~35,750 new deaths over the next two weeks, which means our 7-day moving average for deaths should be dropping from its current 3,151 per day down to about 2,500 per day by Feb 17/18.