diff --git a/libs/ml/include/psemek/ml/neural_net/loss.hpp b/libs/ml/include/psemek/ml/neural_net/loss.hpp
new file mode 100644
index 00000000..31f242dd
--- /dev/null
+++ b/libs/ml/include/psemek/ml/neural_net/loss.hpp
@@ -0,0 +1,19 @@
+#pragma once
+
+#include <vector>
+
+#include <psemek/geom/math.hpp>
+
+namespace psemek::ml
+{
+
+	template <typename T>
+	T l2_loss(std::vector<T> const & x1, std::vector<T> const & x2)
+	{
+		T value = T{0};
+		for (std::size_t i = 0; i < x1.size(); ++i)
+			value += geom::sqr(x1[i] - x2[i]) / T{2};
+		return value;
+	}
+
+}