diff --git a/modules/purchase_trade/fee.py b/modules/purchase_trade/fee.py
index ffbd2a4..76d8645 100755
--- a/modules/purchase_trade/fee.py
+++ b/modules/purchase_trade/fee.py
@@ -319,7 +319,7 @@ class Fee(ModelSQL,ModelView):
                 if self.line:
                     if self.line.purchase.payment_term:
                         beg_date = self.fee_date if self.fee_date else Date.today()
-                        est_date = self.line.purchase.payment_term[0].get_date(beg_date)
+                        est_date = self.line.purchase.payment_term.lines[0].get_date(beg_date)
                         if est_date and beg_date:
                             factor = InterestCalculator.calculate(
                                 start_date=beg_date,
@@ -334,7 +334,7 @@ class Fee(ModelSQL,ModelView):
                 if self.sale_line:
                     if self.sale_line.sale.payment_term:
                         beg_date = self.fee_date if self.fee_date else Date.today()
-                        est_date = self.sale_line.sale.payment_term[0].get_date(beg_date)
+                        est_date = self.sale_line.sale.payment_term.lines[0].get_date(beg_date)
                         if est_date and beg_date:
                             factor = InterestCalculator.calculate(
                                 start_date=beg_date,