信用卡利率计算

突然发现不会算术了，数学公式忘了，结果偷懒搞了下，希望高手给点意见！

#!/bin/bash
COUNT=`cal|awk 'NR==7 {print $NF}'`
read -p "input all of STAGE:" STAGE
read -p "input enchashment:" SUMALL


for i in `seq 1 $STAGE`
do
        echo "#########################################"
        echo -e "THIS IS THE \033[033;40m${i}TH\033[0m TIME AND DETAILS"
        echo "#########################################"


NEXT_SUMALL=`awk "BEGIN{print $SUMALL*(0.9**($i-1))}"`


        echo -e "REMAIN FUND : " "\033[033;40m$NEXT_SUMALL\033[0m"


ACCRUAL=`awk "BEGIN{print $NEXT_SUMALL*0.0005*$COUNT}"`


        echo -e "CURRENT PERIOD ACCRUAL: "  "\033[033;40m$ACCRUAL\033[0m"


        if [[ "$i" == "1" ]];then
                CURRENT=`awk "BEGIN{print $NEXT_SUMALL+$ACCRUAL+$NEXT_SUMALL*0.01}"`
                echo -e "the $i months is "  "\033[033;40m$CURRENT\033[0m"
        elif [[ "$i" > "1" ]];then
                CURRENT=`awk "BEGIN{print $ACCRUAL+$NEXT_SUMALL}"`
                echo -e "the $i months is "  "\033[033;40m$CURRENT\033[0m"
        else
                exit
        fi
done