diff --git a/construction-installment-calculator/index.html b/construction-installment-calculator/index.html
index 6cdd2bd..84cc542 100644
--- a/construction-installment-calculator/index.html
+++ b/construction-installment-calculator/index.html
@@ -454,13 +454,16 @@ function exportExcel() {
   let cumDays = 0, cumTotal = 0, cumNgpm = 0, cumNook = 0;
 
   installments.forEach((inst, i) => {
-    const days   = parseFloat(inst.days) || 0;
-    const pct    = parseFloat(inst.percent) || 0;
+    const days = parseFloat(inst.days) || 0;
+    const pct  = parseFloat(inst.percent) || 0;
+    const isLast = i === installments.length - 1;
     cumDays += days;
-    const total  = Math.round(contract * pct / 100);
-    const ngpm   = Math.round(total * ngpmPct / 100);
-    const nook   = total - ngpm;
+
+    const total = isLast ? (contract - cumTotal) : Math.round(contract * pct / 100);
+    const ngpm  = isLast ? (Math.round(contract * ngpmPct / 100) - cumNgpm) : Math.round(total * ngpmPct / 100);
+    const nook  = total - ngpm;
     cumTotal += total; cumNgpm += ngpm; cumNook += nook;
+
     const delivery = toThaiDate(addDays(startDate, cumDays));
     rows.push([i+1, days, pct, delivery, total, ngpm, nook, cumTotal, cumNgpm, cumNook]);
   });