diff --git a/index.js b/index.js
index bcba7bc..b580ded 100644
--- a/index.js
+++ b/index.js
@@ -141,8 +141,8 @@ function splitPostpaidDetail(str) {
     return retval;
 }
 
-function calculateBaseBillAmount(detailSplitted) {
-    const keywords = ['TAGIHAN', 'DENDA', 'RPPREMI'];
+function calculateBaseBillAmount(detailSplitted, customKeywords) {
+    const keywords = customKeywords || ['TAGIHAN', 'DENDA', 'RPPREMI', 'BIAYA'];
 
     let retval = 0;
     let detailCount = (detailSplitted || []).length;