Tax efficiency: a working definition

The other week, I watched (almost; I read the transcript) a little informational video at Vanguard, where I keep some investments. It was tax season, and so I was interested in what they had to say about tax planning, and I happened across this video. I was perusing through, when one of the characters said this:

...tax efficiency is not about minimizing taxes. It's about maximizing after-tax return.

And my mind expanded.

And he's totally right. See, when tax season is imminent, it's tempting to think about minimizing the amount of tax you're paying. After all, paying out that money hurts!

But the right way to think about it is, instead, to maximize the amount of money you're keeping.

Exhibit A: Mortgages. Mortgages are too often touted in the press as entitling one to the "lucrative" mortgage interest deduction. And it's true: for every dollar you pay in mortgage interest, you can reduce the amount of money you're taxed on by a dollar. Sweet, right?

Well, look at the big picture. For those in the 15% tax bracket, you save fifteen cents of income taxes for every dollar in mortgage interest you pay. While this certainly reduces the burden of mortgage payments somewhat, giving away a dollar to get fifteen cents is hardly a winning strategy. (*)

Conversely, if you pay off your mortgage, you do "lose" the mortgage interest deduction, but you also don't have to pay any mortgage interest. Certainly there's still an argument for keeping a mortgage alive when you can afford to pay it off, but it's not the slam dunk often portrayed in the media. Instead, think about it clearly and run the numbers.

Is tax efficiency around minimizing your taxes? It shouldn't be. Think instead about maximizing returns instead, and that will point you in the right direction.

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* The real impact of the deduction is to lower the effective interest rate of the mortgage, from, say, 4.0% to 3.4%, assuming that (a) you itemize more than the standard deduction already, (b) you aren't in any credit phaseout ranges, and (c) ignoring air resistance.