Disposable income, also known as disposable personal income (DPI), is the amount of money that an individual or household has to spend or save after income taxes have been deducted. - investopedia.com
I think this is very flawed term to use for the money you have left after you have paid your taxes. Disposable in our typical vocabulary is a word used to throw things out.
after-tax-income, would be a better term for this.