diff --git a/src/main/java/calculators/TransactionCalculator.java b/src/main/java/calculators/TransactionCalculator.java
new file mode 100644
index 0000000..741c56a
--- /dev/null
+++ b/src/main/java/calculators/TransactionCalculator.java
@@ -0,0 +1,10 @@
+package calculators;
+
+import java.math.BigDecimal;
+
+public interface TransactionCalculator {
+  public BigDecimal calculateGross();
+  public BigDecimal calculateComission();
+  public BigDecimal calculateTax();
+  public BigDecimal calculateTotal();
+}