房貸攤還如何計算本息

我的房貸是指數型房貸.我該怎麼算出與每月銀行所計算的金額相符.該怎麼算才可以算出每月還的本金跟利息與銀行相同呢?(利率欄才是每月實際還款的利率)麻煩達人教教.我並給我計算公式以下是我2年的還款記錄.當初的借款金額是317萬 付款期數付款日期指標利率利率額外付款合計付款本金利息尚餘本金累積付款12008/5/222.553%2.580%　16930 1011468163159886 1693022008/6/232.600%2.627%　17000 1018268183149704 33930 32008/7/232.600%2.627%　17000 1010568953139599 50930 42008/8/232.600%2.627%　17000 1012768733129472 67930 52008/9/232.660%2.687%　17090 1020468863119268 85020 62008/10/232.660%2.687%　17090 1010569853109163 102110 72008/11/232.660%2.960%　17510 984176693099322 119620 82008/12/232.180%2.480%　16780 942473563089898 136400 92009/1/232.180%2.480%　16780 1039463863079504 153180 102009/2/232.180%2.480%　16780 1041663643069088 169960 112009/3/231.090%1.390%　15210 946457463059624 185170 122009/4/231.090%1.390%　15210 1166635443047958 200380 132009/5/231.090%1.540%　15430 1151839123036440 215810 142009/6/231.090%1.540%　15430 1153338973024907 231240 152009/7/231.090%1.540%　15430 1154838823013359 246670 162009/8/231.090%1.540%　15430 1156338673001796 262100 172009/9/231.090%1.540%　15430 1157838522990218 277530 182009/10/231.090%1.540%　15430 1159338372978625 292960 192009/11/231.090%1.540%　15430 1160738232967018 308390 202009/12/231.020%1.470%　15340 1157337672955445 323730 212010/1/231.020%1.470%　15340 1172036202943725 339070 222010/2/231.020%1.470%　15340 1173436062931991 354410 232010/3/231.020%1.470%　15340 1174835922920243 369750 242010/4/231.020%1.470%　15340 1176335772908480 385090
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