The income of fixed investment fund is the main problem of this example. At present, there are only a handful of open-end funds on the market whose average income exceeds 10 in three years. The income from fixed investment is an average income, so you can invest in some funds whose net value fluctuates greatly. Assuming that the annual income is 6%, the total principal and income of 15 years can reach 300,000.

m= 12a( 1+x)[- 1+( 1+x)^n]/x，

M: Expected income.

A: Monthly fixed investment.

X: one-year rate of return

N: fixed investment period (n power in the formula)