If you want to, you can do the algebra:
FVIF = Future value (of 1) before taxes − taxes
= 1 × (1 + r)ⁿ − tcg × [1 × (1 + r)ⁿ − B]
= (1 + r)ⁿ − tcg(1 + r)ⁿ + tcgB
= (1 + r)ⁿ(1 – tcg) +tcgB
There’s your formula. And, as I tell my candidates, do your level best to blot it from your mind! Do not memorize this formula; it’s a waste of precious neurons! (I don’t know about you, but I have only about two neurons left; I cannot afford to waste them on anything.) What you should do is understand the formula: it’s the first line of the algebra: future value before taxes less taxes. On the exam, if you need to calculate it, you should be able to calculate it easily without memorizing a formula.
You have $1 million growing for 20 years at 5%. The tax basis is $200,000, and the capital gains tax rate is 25%. What’s the final value?
Future value before taxes = $1,000,000(1.05)²º = $2,653,298.
Capital gain = $2,653,298 − $200,000 = $2,453,298.
Capital gains tax = $2,453,298 × 25% = $613,324.
Future value after taxes = $2,653,298 − $613,324 = $2,039,974.