Simple formula for four years of HPSP is that you take the total scholarship amount spent, divided into the number of days of ADSO to come up with a per-day dollar figure. Then subtract the number of ADSO days paid back leaving X amount of days still owed at X amount of dollars per day.
Scholarship (tuition, fees, books and stipend) = ~$250k
Four year scholarship is 365 days X 4 = 1460 days
250K divided by 1460 = ~$171.25 per day spent
Now, if after training, you have paid back say exactly two years of ADSO, you still owe 730 days, but you have burned $125K worth of paid entitlements. So, 730 days multiplied by the 171.25 owed will equal approximately the 125K still owed in entitlements. Again, this is an over simplification. There are always odd days. It is never exactly one or two years it is always one year, two months and 13 days or some such, not to mention you are paying back time until the date on your separation order.
We must also consider GMO or F/S time before residency as payback, and the number of days owed is reduced accordingly. If you add in Service Academy time, or ROTC it will change the formula. The first obligation incurred is the first paid back. So, if after training, you owe for Service Academy or ROTC, that obligation must be considered before the HPSP obligation/money.
The Army Auditing Agency has recently completed a study concerning the recoupment of funds for ROTC, USMA and HPSP, I am assuming that ROTC and USMA were able to provide some sort of a per day dollar figure. On the other hand, the only thing I’ve ever seen from USUHS is a very old article in Time Magazine that basically states the cost of attending is some sort of secret.
http://nation.time.com/2012/06/22/usuhs-no-wonder-some-pronounce-it-useless/