This is a relatively simple financial math question that most people I’ve asked have gotten wrong.

Answers have ranged from less than 8.8% – since only capital gains are being taxed (huh?) … 8.8% – because that’s how much the marginal rate is going up … to more than 8.8% – “otherwise you wouldn’t be asking the question”.

First, what’s magic about 8.8%?

Well, Obama did what he promised and jacked capital gains tax rates from 15% to 20% … and, don’t forget ObamaCare has a 3.8% non-payroll payroll tax on investment income starting in 2013.

So, the effective capital gains tax rate is going from 15% to 23.8% … a delta of 8.8%.

**That 8.8% increase will cut after-tax capital gains by 10.35% !**

**If you don’t believe me, here’s he math …**

You can either watch the tutorial or ship down to the recap/

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**Recap**

Assume that you bought a stock for $750 and sold it for $1,000 … netting a **$250 pre-tax gain**.

If the capital gains tax is **15%**, you pay $37.50 in taxes … netting you, after taxes, **$212.50**.

If the capital gains tax is **23.8%**, you pay $59.50 in taxes … netting you, after taxes, **$190.50**.

The difference, is **$22** ($212.50 less $190.50 … or simply, 8.8% times $250).

So the percentage drop in after-tax net gains is **10.35%** ($22 divided by $212.50)

Note that that percentage stays constant at **10.35%** regardless of the size of the gain – in absolute or relative to proportionate cost basis.

That’s not a coincidence, it’s math.

With a capital gains tax rate of 15%, the after tax gain is simply 1 minus the tax rate times the nominal gain … 1 minus 15% is **85%**.

With a capital gains tax rate of 23.8%, the after tax gain is simply 1 minus that tax rate times the nominal gain … 1 minus 23.8% is** 76.2%**.

The difference is still **8.8%**, but the denominator of the change ratio is is 85%, not 100% … and, 8.8% divided by 85% is **10.35%**.

Again, that answer is generalizable … not specific to this example.

Q.E.D.

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