After taxes and living expenses wouldn’t most MD/PhD grads, esp in high COL areas where many of the top schools are, have ~$0 in the bank after graduating?
Here's how the math works:
At the end of med school, the MD-PhD has $0 in debt but also $0 net worth.
The MD-only has ~300g in debt.
At the end of 5- year residency (let's say they both go into something nice and lucrative, like diagnostic radiology or rad onc or ortho), the MD-PhD has $0 in debt--perhaps if he pinches himself he saves 5g per year in a Roth IRA for 5 years, plus compounding, but let's just discount it.
The MD-only has ~450g in debt because the 300g debt now compounded at a 6-8% interest rate.
At the end of 5 years post-residency, the MD-PhD and the MD-only each saved about 100g a year, which is not unreasonable.
Simplistically, neglect tax, interests, investment yield etc., at this point the MD-PhD now has a net worth of 500g. The MD-only has 50g net worth.
Assuming a 7% rate of return investing in broad market index fund, at the end of 25 years (assuming a 30-year career), that 500g is now 2.7M. The 50g? 270g.
Now let's say the MD only works 4 years extra, since she started early and graduated early (I don't know why she would tho, since the total duration of employment AFTER training is exactly the same). She saves another 100g per year at the end of her career. The total dollar differential is 2.7M - 670g + ~ $80g (4 years of compounding of 270g) = ~ 1.8 M.
Now, if you save 100g per year consistently for 30 years as an ortho, your net worth would be > 10M, so that 1-2M net worth difference wouldn't really matter--especially if you would've hated doing a PhD in your 20s vs. either doing something else or just retire 4 years early, but just on a financial level, the differential is very real. PSLF changes things somewhat, but the gestalt remains the same. The only way MD-only would beat MD-PhD is if MD-only makes a series of choices later that prove a much higher overall income and savings, which on the whole is true, since most MD-PhDs go into research-oriented jobs or academia, which means they take a substantial job cut over the length of the career. But if you don't do that you are much much better off doing the MD-PhD than MD-only.
I'm being extreme to illustrate the point: this difference can easily be a million or more over 30 years.
This math also shows that the total financial return of value for the PhD years is very high. Even not counting the salary increase, just purely based on tuition, the PhD gives 100g *post-tax* savings with a 35k living standard. This means a pre-tax total income in the 150k+ level for 3-4 years. The only jobs that pay 150k+ a year for a fresh undergrad are 1) investment banking 2) management consulting or 3) big tech.