diff --git a/test/growth/growth_test.exs b/test/growth/growth_test.exs
new file mode 100644
index 0000000..3752689
--- /dev/null
+++ b/test/growth/growth_test.exs
@@ -0,0 +1,131 @@
+defmodule GrowthTest do
+  @moduledoc false
+
+  use ExUnit.Case, async: true
+
+  doctest Growth
+
+  @child %{
+    name: "Jane Doe",
+    gender: :female,
+    date_of_measurement: Date.utc_today(),
+    age_in_days: 91,
+    weight: 5.84,
+    height: 59.78,
+    head_circumference: 39.51,
+    arm_circumference: 13.02,
+    subscapular_skinfold: 7.79,
+    triceps_skinfold: 9.75
+  }
+  @child_date_of_birth Date.shift(@child.date_of_measurement, day: @child.age_in_days * -1)
+
+  describe "new/4" do
+    test "create a new growth measurement" do
+      growth =
+        Growth.new(@child.name, @child.gender, @child_date_of_birth,
+          date_of_measurement: @child.date_of_measurement,
+          weight: @child.weight,
+          height: @child.height,
+          head_circumference: @child.head_circumference,
+          arm_circumference: @child.arm_circumference,
+          subscapular_skinfold: @child.subscapular_skinfold,
+          triceps_skinfold: @child.triceps_skinfold
+        )
+
+      assert @child.name == growth.name
+      assert @child.gender == growth.gender
+      assert @child_date_of_birth == growth.date_of_birth
+      assert @child.date_of_measurement == growth.date_of_measurement
+      assert @child.age_in_days == growth.age_in_days
+      assert 13 == growth.age_in_weeks
+      assert 2 == growth.age_in_months
+      assert @child.weight == growth.weight
+      assert @child.height == growth.height
+      assert @child.head_circumference == growth.head_circumference
+      assert @child.arm_circumference == growth.arm_circumference
+      assert @child.subscapular_skinfold == growth.subscapular_skinfold
+      assert @child.triceps_skinfold == growth.triceps_skinfold
+    end
+  end
+
+  describe "with_bmi/1" do
+    test "calculate bmi from measurement" do
+      growth =
+        %Growth{
+          name: @child.name,
+          gender: @child.gender,
+          date_of_birth: @child_date_of_birth,
+          date_of_measurement: @child.date_of_measurement,
+          weight: @child.weight,
+          height: @child.height,
+          head_circumference: @child.head_circumference,
+          arm_circumference: @child.arm_circumference,
+          subscapular_skinfold: @child.subscapular_skinfold,
+          triceps_skinfold: @child.triceps_skinfold
+        }
+        |> Growth.with_age_in_days()
+        |> Growth.with_age_in_weeks()
+        |> Growth.with_age_in_months()
+        |> Growth.with_bmi()
+
+      assert 16.341842694989243 == growth.bmi
+    end
+  end
+
+  describe "with_results/1" do
+    test "calculate z-score and percentiles from measurement" do
+      growth =
+        %Growth{
+          name: @child.name,
+          gender: @child.gender,
+          date_of_birth: @child_date_of_birth,
+          date_of_measurement: @child.date_of_measurement,
+          weight: @child.weight,
+          height: @child.height,
+          head_circumference: @child.head_circumference,
+          arm_circumference: @child.arm_circumference,
+          subscapular_skinfold: @child.subscapular_skinfold,
+          triceps_skinfold: @child.triceps_skinfold,
+          results: []
+        }
+        |> Growth.with_age_in_days()
+        |> Growth.with_age_in_weeks()
+        |> Growth.with_age_in_months()
+        |> Growth.with_bmi()
+        |> Growth.with_results()
+
+      assert [
+               day: {9.496948997971584e-4, 0.5003788733920584},
+               week: {9.496948997971584e-4, 0.5003788733920584},
+               month: {1.0060928051683196, 0.8428145353253619}
+             ] == Keyword.get(growth.results, :weight)
+
+      assert [
+               day: {0.0012831717968983271, 0.5005119113423219},
+               week: {0.0012831717968983271, 0.5005119113423219},
+               month: {1.3322618635180914, 0.9086129228760054}
+             ] == Keyword.get(growth.results, :height)
+
+      assert [
+               day: {-0.007440424136462911, 0.4970317276150869},
+               week: {-0.007440424136462911, 0.4970317276150869},
+               month: {0.3827194919327071, 0.6490361198066796}
+             ] == Keyword.get(growth.results, :bmi)
+
+      assert [
+               day: {-0.008864109494641385, 0.4964637782528006},
+               week: {-0.008864109494641385, 0.4964637782528006},
+               month: {1.0380198575748647, 0.8503695948597997}
+             ] == Keyword.get(growth.results, :head_circumference)
+
+      assert [day: {-0.004182676756535293, 0.49833135826198854}] ==
+               Keyword.get(growth.results, :arm_circumference)
+
+      assert [day: {0.001811404894950268, 0.5007226456043324}] ==
+               Keyword.get(growth.results, :subscapular_skinfold)
+
+      assert [day: {-0.0019309186728254878, 0.49922967538007906}] ==
+               Keyword.get(growth.results, :triceps_skinfold)
+    end
+  end
+end