diff --git a/marge.js b/marge.js
new file mode 100644
index 0000000..900df6d
--- /dev/null
+++ b/marge.js
@@ -0,0 +1,5 @@
+// Calcul de la marge d'un bookmaker
+function marge(cotes) {
+  return cotes.reduce((s, c) => s + 1 / c, 0) - 1;
+}
+module.exports = marge;