The account has "not lost much" for several consecutive months, but the balance has quietly become smaller. The problem often lies in the cost rate. This article explains the algorithm of cost rate, why it affects the mathematical results of account growth in the direction of compound interest, why no matter how high the winning rate is, costs must be covered first, and how to convert spreads, handling fees, overnight interest and slippage into consumption ratios at the account level. It also gives four feasible cost reduction directions of controlling frequency, selecting periods with good liquidity, standardizing order types, and pooling funds to make the growth line of the account truly upward.