diff --git a/js/tests/dog-years_test.js b/js/tests/dog-years_test.js
new file mode 100644
index 00000000..ed11c50a
--- /dev/null
+++ b/js/tests/dog-years_test.js
@@ -0,0 +1,13 @@
+export const tests = []
+const t = (f) => tests.push(f)
+
+t(({ eq }) => eq(dogYears('earth', 1000000000), 221.82))
+t(({ eq }) => eq(dogYears('mercury', 2134835688), 1966.16))
+t(({ eq }) => eq(dogYears('venus', 189839836), 68.45))
+t(({ eq }) => eq(dogYears('mars', 2129871239), 251.19))
+t(({ eq }) => eq(dogYears('jupiter', 901876382), 16.86))
+t(({ eq }) => eq(dogYears('saturn', 2000000000), 15.07))
+t(({ eq }) => eq(dogYears('uranus', 1210123456), 3.19))
+t(({ eq }) => eq(dogYears('neptune', 1821023456), 2.45))
+
+Object.freeze(tests)
diff --git a/subjects/dog-years.en.md b/subjects/dog-years.en.md
new file mode 100644
index 00000000..2424b99d
--- /dev/null
+++ b/subjects/dog-years.en.md
@@ -0,0 +1,21 @@
+## Dog Years
+
+### Instructions
+
+Someone once said that a dog makes 7 years for each human year.
+
+Create a `dogYears` function that if given a planet name and an age in seconds,
+calculates how old a dog would be on the given planet.
+
+- Earth: orbital period 1.0 Earth years, 365.25 Earth days, or 31,557,600 seconds
+- Mercury: orbital period 0.2408467 Earth years
+- Venus: orbital period 0.61519726 Earth years
+- Mars: orbital period 1.8808158 Earth years
+- Jupiter: orbital period 11.862615 Earth years
+- Saturn: orbital period 29.447498 Earth years
+- Uranus: orbital period 84.016846 Earth years
+- Neptune: orbital period 164.79132 Earth years
+
+So if you were told someone that their dog were 1,000,000,000 seconds old, you should be able to say that the dog is 221.83 Earth-years old.
+
+You will have to format the number so that the result is rounded like the example above.