So much has already been said about Barack Obama’s speaking fees.

So much — except for the one thing that should actually matter.

Barack and Michelle Obama are residents of Washington, D.C., which means they are subject to District of Columbia income taxes. Those top out at 8.95%.

They will, of course, also be subject to the far heavier federal tax rate, which tops out at 39.6%.

Dollars to doughnuts that the former president and first lady will be in the highest income brackets. That means each dollar of extra income will be subject to a combined marginal rate of tax of about 45% (it’s not 49% because the D.C. tax, which is deductible, should reduce the federal tax liability).

So to put this in terms that even haters can understand, when Obama gives a speech and gets paid $400,000, he generates $180,000 in taxes, most of it federal.

Not bad for what is, when you include speech writing, preparation and travel, probably a few days’ work.

Let’s be even clearer.

A first-year private in the U.S. Army earns $18,700. So Obama’s one speech to Wall Street will pay the salaries of 10 of them for the year. (OK, for simplicity’s sake, I’m ascribing all his tax to the federal level. This is merely an illustration. You can run numbers based on Washington police officers, local services or whatever.)

Or, as the Kaiser Foundation calculates, Medicaid’s annual bill for a recipient with disabilities is $16,643. So Obama just paid the full year’s Medicaid bill for 11 people with disabilities.

Or, to put it another way, the average Pell grant to help kids pay for college works out to $3,724, according to the College Board. So Obama’s speech just paid for a full year’s Pell grants for 48 kids.

No doubt this was what right-wing gadfly Dinesh D’Souza was talking about when he tweeted, about Obama’s fees, “His service to the poor and needy continues.” (D’Souza is always right, by the way. For example, his movie “2016: Obama’s America” correctly predicted last year’s massive financial collapse.)

Actually, Obama is giving two speeches for $800,000, so we have to double everything. With those two speeches he’s paying for 20 soldiers, or 22 people with disabilities, or 96 Pell grants.

Naturally, this is true of all earners, especially high earners, regardless of politics.

I’ve said it before, and I’ll say it again. We don’t have a right-wing (or left-wing) problem in this country. We have a facts and logic problem. Grown men and women think, talk and act in ways that would have earned a 10-year old an “F” where I went to school.

Don’t get me started on right wingers complaining that Obama is charging the market rate for his services.

Or on left wingers complaining that someone who pays the top rate of income tax has gone out and earned lots of money. Er ... how else did they expect to pay for programs?

Meanwhile, Sen. Elizabeth Warren says she is “troubled” by Obama’s speaking fee. Naturally. She may run for president in 2020, and she knows that a good chunk of votes are controlled by angry people who don’t understand economics.

So it would probably be rude of me to point out that when she was at Harvard, she billed the university for $326,000 a year in compensation — or roughly the cost of 88 Pell grants.

Also read: Elizabeth Warren says Obama got it wrong: It’s worse than Americans realize