The difference between discretionary fund and discretionary income is clear. Discretionary fund is a money allocated or budgeted for something that is not really necessary or investment, it's just a fund for hanging out with friends to have fun, or a money for dinning out, or a money for travels, while discretionary income is a leftover money after you must have settled your basic needs and expenses either for the week or for the month. And your Discretionary income is the money you will use to invest in bitcoin and to build your emergency fund and backup fund.