If a person has a taxable income of 270,000 with an increase of 60,000 in expenses. The taxable income after the change would be 210,000. The income tax with a tax rate of 40 percent would be 84,000 and the income after the tax would be 126,000. But what would be the after cost of the increased expense?

For tax-deductible expenses, the after-tax cost is: expense x (1-taxrate). In this case, $60K x (1-0.4) = $36K. This assumes that the tax rate stays at the flat 40%.

Agree!