diff --git a/examples/darth-vader.txt b/examples/darth-vader.txt
new file mode 100644
index 0000000..c7290f2
--- /dev/null
+++ b/examples/darth-vader.txt
@@ -0,0 +1,29 @@
+Name: Darth Vader
+Author: HumanPowerPerformance.com
+Description:
+  Sign up for coaching with HumanPowerPerformance.com and get custom workouts and training plans
+
+Warmup: 5:00 55%
+
+Rest: 3:00 82%
+Interval: 00:20 130%
+Rest: 3:00 82%
+Interval: 00:20 130%
+Rest: 3:00 82%
+Interval: 00:20 130%
+Rest: 3:00 82%
+Interval: 00:20 130%
+Rest: 3:00 82%
+Interval: 00:20 130%
+Rest: 3:00 82%
+Interval: 00:20 130%
+Rest: 3:00 82%
+Interval: 00:20 130%
+Rest: 3:00 82%
+Interval: 00:20 130%
+Rest: 3:00 82%
+Interval: 00:20 130%
+Rest: 3:00 82%
+Interval: 00:20 130%
+
+Cooldown: 5:00 55%
diff --git a/package.json b/package.json
index 3f94ffb..569207f 100644
--- a/package.json
+++ b/package.json
@@ -5,6 +5,7 @@
   "scripts": {
     "lint:ts": "tsc --noEmit",
     "test": "ts-node src/index.ts examples/threshold-pushing.txt",
+    "test:2": "ts-node src/index.ts examples/darth-vader.txt",
     "format:js": "prettier --write src/"
   },
   "devDependencies": {
diff --git a/src/index.ts b/src/index.ts
index 8d4fcec..ae63ec2 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,6 +1,7 @@
 import * as fs from "fs";
 import { parse } from "./parser";
 import { tokenize } from "./tokenizer";
+import { tss } from "./tss";
 
 const filename = process.argv[2];
 
@@ -10,4 +11,15 @@ const file = fs.readFileSync(filename, "utf8");
 
 const workout = parse(tokenize(file));
 
-console.log(workout);
+console.log(workout.intervals);
+
+workout.intervals.forEach((interval, i) => {
+  console.log(`#${i} TSS: ${tss([interval])}`);
+});
+
+console.log("Total TSS: " + tss(workout.intervals));
+
+const duration =
+  workout.intervals.map(({ duration }) => duration).reduce((a, b) => a + b, 0) /
+  60;
+console.log(`Total duration: ${duration} minutes`);
diff --git a/src/tss.ts b/src/tss.ts
new file mode 100644
index 0000000..2398e66
--- /dev/null
+++ b/src/tss.ts
@@ -0,0 +1,37 @@
+import { Interval } from "./ast";
+
+// Training Stress Score formula from Training and Racing with a Power Meter:
+//
+// TSS = (s * W * IF) / (FTP * 3600) * 100
+//
+// s - duration in seconds
+// W - power in watts
+// IF - intensity factor (power / FTP)
+
+const steadyTss = (duration: number, power: number): number => {
+  const intensity = power / 100;
+
+  return ((duration * intensity * intensity) / 3600) * 100;
+};
+
+const rangeTss = (duration: number, from: number, to: number): number => {
+  let score = 0;
+  const step = 1;
+  for (let i = 0; i < duration; i += step) {
+    let power = from + (to - from) * (i / duration);
+    score += steadyTss(step, power);
+  }
+  return score;
+};
+
+const intervalTss = ({ duration, power }: Interval): number => {
+  if (power.from === power.to) {
+    return steadyTss(duration, power.from);
+  } else {
+    return rangeTss(duration, power.from, power.to);
+  }
+};
+
+export const tss = (intervals: Interval[]): number => {
+  return intervals.map(intervalTss).reduce((a, b) => a + b, 0);
+};