[tallanvor]

I was taught that you should estimate a 4% rate of return, which means Harvard's endowment can cover around 40% of their budget. Much of the remainder will come through research grants, and a rather small percentage will be tuition and fees.

[laGrenouille]

Yes, that's what I learned as well. And that's actually close to what Harvard reported using last year ($2.1 billion from the endowment; 40% of the budget).

I was only using the more aggressive number as a thought experiment to the original poster about what it would take the cover the entire operating budget.