The income of the fund's fixed investment is related to the amount of fixed investment in each period, the annual rate of return of the fund and the fixed investment time. The fixed investment of each period of the fund is the same, so the subscription fee to be deducted in each period is also the same. There is a formula for calculating the income of the fund's fixed investment.

Calculation formula of fund fixed investment income:

m=a( 1+x)[- 1+( 1+x)^n]/x

Among them, m represents the total amount (including income and principal) after the fixed investment for n years, a represents the amount invested every year (for example, 200 yuan is invested every month, a = 2,400 yuan), b represents the annual rate of return (for example, annual income 15%, b = 0. 15), and n represents the n power (because it cannot be marked, it has to be expressed this way).

Suppose a fund invests in 200 yuan every month (2400 yuan per year), and the annual rate of return is 15%. After one year of investment, the income plus principal is:

2400 ( 1+ 15%) [- 1+( 1+ 15%) 1]/ 15% = 2400× 1.

Income = 2760 yuan -200× 12 yuan = 360 yuan.

That is, a certain fund will make a fixed investment in 200 yuan every month, and it will make a profit in 360 yuan one year later.