TSS Calculator

Training Stress Score (TSS) is a numerical measure that quantifies how much physiological stress a single workout places on your body. Developed by exercise scientist Dr. Andrew Coggan and introduced through the TrainingPeaks platform, TSS combines workout duration and intensity into one number, making it far easier to compare the relative demands of wildly different sessions — a two-hour endurance ride versus a 40-minute threshold interval set, for example.

The core idea is elegantly simple: one hour performed at exactly your threshold effort (Functional Threshold Power, Lactate Threshold Heart Rate, or Threshold Pace, depending on your sport) equals 100 TSS points. Every workout is then scored relative to that benchmark. A recovery spin might net 40 TSS; an all-day gran fondo could earn 400 or more. Because TSS is normalized against your personal threshold, it adjusts automatically as your fitness improves — a fitter athlete and a beginner doing the same ride will accumulate different TSS values if their FTPs differ.

TSS is the foundation of modern endurance periodization. Coaches use it to build ATL (Acute Training Load), CTL (Chronic Training Load), and TSB (Training Stress Balance) models that predict fatigue, fitness, and form. Without TSS as a common currency, comparing the load of swimming, cycling, and running sessions would require separate tracking systems. With it, a triathlete can manage combined training stress across all three disciplines in a single weekly total.

This TSS calculator supports three calculation methods: power-based TSS for cycling (the most precise method), heart-rate TSS (hrTSS) for sessions without a power meter, and running TSS (rTSS) for paced running workouts. Each method relies on a different threshold metric — FTP, LTHR, or threshold pace — but all produce scores on the same 0–500+ scale.

Each of the three modes in this calculator uses a distinct formula, but all share the same underlying logic: time multiplied by the square of intensity relative to threshold, scaled to 100 for a one-hour threshold effort.

Power-Based TSS (Cycling)

Power TSS is the most accurate method because power meters measure actual mechanical output. The formula uses Normalized Power (NP) rather than average power, because NP accounts for the metabolic cost of variable-intensity riding (surges, sprints, and descents).

The Intensity Factor (IF) is computed first as NP ÷ FTP. TSS then equals the duration in seconds multiplied by NP and IF, divided by FTP × 3600, multiplied by 100. Algebraically this simplifies to (durationMin × 60 × NP × IF) ÷ (FTP × 3600) × 100.

Heart Rate TSS (hrTSS)

When no power meter is available, heart rate relative to Lactate Threshold Heart Rate (LTHR) acts as a proxy. The HR ratio (avgHR ÷ LTHR) is squared and then scaled: hrTSS = durationMin × (avgHR ÷ LTHR)² × 100 ÷ 60. Because heart rate drifts upward during prolonged effort (cardiac drift), hrTSS tends to slightly overestimate stress in very long sessions and underestimate it in short hard intervals.

Running TSS (rTSS)

Running TSS flips the pace ratio because slower pace means higher time per kilometre. The Intensity Factor for running is thresholdPace ÷ runPace (a number less than 1.0 when running slower than threshold). Total run duration in minutes is distance × runPace. rTSS is then: (distance × runPace × IF² × 100) ÷ 60.

All three methods converge at 100 TSS for exactly one hour at threshold — an IF of 1.0 for the full 60 minutes — giving coaches a consistent scale regardless of sport or measurement tool.

A raw TSS number only becomes meaningful once you understand what recovery demand it implies. The five zones used in this calculator map directly onto the physiological cost of the workout and the time your body needs to fully adapt before performing again at high intensity.

These thresholds are general guidelines; individual response to training varies considerably based on training age, sleep quality, nutrition, and life stress. A beginner cyclist may need three days to recover from a 120-TSS ride that an elite athlete absorbs overnight. Use the recovery time estimates as a starting framework, then adjust based on your own performance data and subjective fatigue ratings.

While a single workout's TSS tells you how hard today was, weekly TSS totals reveal whether your overall training load is building fitness or risking overtraining. Structured periodization divides the training year into phases, each with a target weekly TSS range that matches its goals.

Base phase (300–500 TSS/week): The foundation block focuses on aerobic development at low to moderate intensity. Most sessions fall below 70% of FTP or LTHR. The relatively modest TSS target allows consistent week-over-week accumulation without accumulating excessive fatigue.

Build phase (500–700 TSS/week): Intensity increases as the athlete adds tempo, sweet-spot, and interval work. The higher TSS reflects more time spent near or above threshold. Week-to-week variability grows: hard weeks may hit 700 followed by a recovery week at 300.

Peak phase (600–900 TSS/week): The final high-load block before a target event. Back-to-back quality sessions, race simulations, and sustained high-intensity work push CTL to its season high. Overreaching is intentional here — provided sufficient recovery follows.

Recovery phase (200–300 TSS/week): Scheduled after hard blocks or target events. Volume and intensity drop sharply to allow super-compensation. Skipping recovery weeks is the most common mistake among self-coached athletes; TSS makes the under-loading deliberate and measurable rather than accidental.

A sensible progression rule: increase weekly TSS by no more than 5–10% per week within a block, and schedule a recovery week every third or fourth week where TSS drops to 50–60% of the previous week. This pattern mirrors the overload-recovery cycles that drive long-term adaptation.

TSS becomes truly powerful when accumulated over time in the Performance Management Chart (PMC), which tracks three rolling averages derived entirely from daily TSS values.

Chronic Training Load (CTL) is a 42-day exponentially weighted moving average of daily TSS. It represents long-term fitness — the higher your CTL, the more total training your body has absorbed and adapted to. CTL moves slowly; it takes weeks of consistent training to raise it meaningfully.

Acute Training Load (ATL) is a 7-day exponentially weighted moving average. It represents short-term fatigue — how hard you have trained in the past week. ATL responds quickly to changes in daily TSS: a big week spikes ATL sharply while a recovery week drops it fast.

Training Stress Balance (TSB), often called "form," is simply CTL minus ATL. A positive TSB means you are fresher than your fitness level — well-rested and ready to perform. A negative TSB means fatigue exceeds fitness — you are digging deeper than your body has adapted to. Elite athletes typically target a TSB of +10 to +25 on race day, achieved by tapering (reducing ATL) while keeping CTL high.

Managing the interplay between CTL, ATL, and TSB is the core task of evidence-based training periodization. Use the CTL/ATL/TSB calculator on this site to model your fitness trajectory alongside this TSS calculator.

The Intensity Factor (IF) is an intermediate calculation that appears in every TSS formula, and understanding it independently helps you gauge workout quality at a glance. IF is the ratio of the workout's normalized intensity to your threshold — whether that is NP/FTP for cycling, avgHR/LTHR for heart rate sessions, or thresholdPace/runPace for running.

An IF of 1.0 means you averaged exactly threshold effort for the entire session. An IF of 0.75 is a comfortable endurance pace; 0.85 is solid tempo territory; 0.95 suggests a very hard sustained effort just below threshold; and an IF above 1.0 indicates the workout averaged above threshold, which is only sustainable for short durations (typically under 60 minutes for power-based efforts).

IF interacts multiplicatively with duration in the TSS formula — because TSS uses IF squared (embedded via NP × IF), even small changes in IF have large effects on TSS. Riding at IF 0.90 for 90 minutes produces substantially more TSS than riding at IF 0.75 for the same duration, even though the time is identical. This is why threshold and above-threshold workouts are so physiologically costly relative to their duration, and why easy aerobic sessions can be extended considerably without accumulating dangerous amounts of stress.