diff --git a/Net.cpp b/Net.cpp
index 7daa4eb..3e9f200 100644
--- a/Net.cpp
+++ b/Net.cpp
@@ -59,7 +59,7 @@ std::vector<double> Net::getOutput()
 
 void Net::backProp(const std::vector<double> &targetValues)
 {
-	const Layer &outputLayer = back();
+	Layer &outputLayer = back();
 
 	if (targetValues.size() != outputLayer.size())
 	{
@@ -67,12 +67,30 @@ void Net::backProp(const std::vector<double> &targetValues)
 	}
 
 	std::vector<double> resultValues = getOutput();
-
+	unsigned int numResultValues = resultValues.size();
 	double rmsError = 0.0;
-	for (unsigned int i = 0; i < resultValues.size(); ++i)
+
+	for (unsigned int i = 0; i < numResultValues; ++i)
 	{
 		double delta = resultValues[i] - targetValues[i];
 		rmsError += delta * delta;
 	}
-	rmsError = sqrt(rmsError / resultValues.size());
+
+	rmsError = sqrt(rmsError / numResultValues);
+
+	for (unsigned int i = 0; i < numResultValues; ++i)
+	{
+		outputLayer[i].calcOutputGradients(targetValues[i]);
+	}
+
+	for (auto it = end() - 1; it != begin(); --it)
+	{
+		Layer &hiddenLayer = *it;
+		Layer &prevLayer = *(it - 1);
+
+		for (auto neuron : hiddenLayer)
+		{
+			//neuron.calcHiddenGradients(prevLayer);
+		}
+	}
 }
diff --git a/Neuron.cpp b/Neuron.cpp
index 3983237..21cb67d 100644
--- a/Neuron.cpp
+++ b/Neuron.cpp
@@ -4,6 +4,7 @@
 
 Neuron::Neuron(double value)
 	: outputValue(value)
+	, gradient(0)
 {
 
 }
@@ -52,3 +53,10 @@ double Neuron::getOutputValue() const
 {
 	return outputValue;
 }
+
+void Neuron::calcOutputGradients(double targetValue)
+{
+	double delta = targetValue - outputValue;
+	gradient = delta * transferFunctionDerivative(outputValue);
+}
+
diff --git a/Neuron.h b/Neuron.h
index 3aecfd3..42d5ad1 100644
--- a/Neuron.h
+++ b/Neuron.h
@@ -7,6 +7,7 @@ class Neuron
 private:
 	double outputValue;
 	std::vector<double> outputWeights;
+	double gradient;
 
 public:
 	Neuron(double value = 1.0);
@@ -18,4 +19,7 @@ public:
 	double getWeightedOutputValue(unsigned int outputNeuron) const;
 	void createRandomOutputWeights(unsigned int numberOfWeights);
 	double getOutputValue() const;
+
+	void calcOutputGradients(double targetValue);
+	//void calcHiddenGradients(const Layer &prevLayer);
 };