diff --git a/LICENSE.md b/LICENSE.md
new file mode 100644
index 0000000..b7532ea
--- /dev/null
+++ b/LICENSE.md
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2022 Pascal Burlet
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
index daddc48..211e0c1 100644
--- a/README.md
+++ b/README.md
@@ -61,3 +61,9 @@ You're welcome to use it in commercial, closed-source, open source, free or any
 
 ## Warranty
 The code comes with no warranty of any kind. I hope it'll be useful to you (it certainly is to me), but I make no guarantees regarding its functionality or otherwise.
+
+## Donations
+
+You really don't have to pay anything to use this package. But if you feel generous today and would like to donate because this package helped you so much, here's a PayPal donation link: https://www.paypal.com/donate/?hosted_button_id=JYL8DBGA2X4YQ
+
+or just buy me a hot chocolate: https://www.buymeacoffee.com/paescebu
\ No newline at end of file
diff --git a/Sources/PolynomialRegressionSwift/PolynomialRegression.swift b/Sources/PolynomialRegressionSwift/PolynomialRegression.swift
index 7e48d76..4f21ae9 100644
--- a/Sources/PolynomialRegressionSwift/PolynomialRegression.swift
+++ b/Sources/PolynomialRegressionSwift/PolynomialRegression.swift
@@ -128,6 +128,29 @@ public class PolynomialRegression {
 
         return b
     }
+	
+	public static func calculateResidualSumOfSquares(ofPoints points: [CGPoint], withCoefficients coefficients: [Double]) -> Double? {
+		guard points.count > 1 else {
+			return nil
+		}
+		
+		guard coefficients.count > 1 else {
+			return nil
+		}
+				
+		let xValuesOfPoints = points.map { Double($0.x) }
+		let yValuesOfPoints = points.map { $0.y }
+				
+		let yPolynomialResults = vDSP.evaluatePolynomial(usingCoefficients: coefficients.reversed(), withVariables: xValuesOfPoints )
+		
+		var sumOfSquares: Double = 0
+		
+		for (yPoly, yPoint) in zip(yPolynomialResults, yValuesOfPoints) {
+			sumOfSquares += Double(pow(yPoly - yPoint, 2))
+		}
+		
+		return sumOfSquares
+	}
 
     public enum LAPACKError: Swift.Error {
         case internalError
diff --git a/Tests/PolynomialRegressionSwiftTests/PolynomialRegressionTests.swift b/Tests/PolynomialRegressionSwiftTests/PolynomialRegressionTests.swift
index 4ee5311..8a380b4 100644
--- a/Tests/PolynomialRegressionSwiftTests/PolynomialRegressionTests.swift
+++ b/Tests/PolynomialRegressionSwiftTests/PolynomialRegressionTests.swift
@@ -97,4 +97,26 @@ class PolynomialRegressionTests: XCTestCase {
         regression = PolynomialRegression.regression(withPoints: [CGPoint(x: 0, y: 0)], degree: 1)
         XCTAssertEqual(regression, nil)
     }
+	
+	func testPolynomialRegressionSumOfSquares(){
+		let regression = PolynomialRegression.regression(withPoints: points, degree: 3)
+		let sumOfSquare = PolynomialRegression.calculateResidualSumOfSquares(ofPoints: points, withCoefficients: regression!)
+		XCTAssertEqual(sumOfSquare!, 551.0158144934717)
+	}
+	
+	func testPolynomialRegressionSumOfSquaresFails(){
+		let regression = PolynomialRegression.regression(withPoints: points, degree: 3)
+		
+		var sumOfSquare = PolynomialRegression.calculateResidualSumOfSquares(ofPoints: [], withCoefficients: regression!)
+		XCTAssertEqual(sumOfSquare, nil)
+
+		sumOfSquare = PolynomialRegression.calculateResidualSumOfSquares(ofPoints: points, withCoefficients: [])
+		XCTAssertEqual(sumOfSquare, nil)
+		
+		sumOfSquare = PolynomialRegression.calculateResidualSumOfSquares(ofPoints: [CGPoint(x: 0, y: 0)], withCoefficients: regression!)
+		XCTAssertEqual(sumOfSquare, nil)
+		
+		sumOfSquare = PolynomialRegression.calculateResidualSumOfSquares(ofPoints: [], withCoefficients: [])
+		XCTAssertEqual(sumOfSquare, nil)
+	}
 }