How do I work out my triathlon training zones?

Test one threshold per discipline and derive everything from it: Critical Swim Speed from a 400 m and 200 m time trial, FTP from a ramp or 20-minute bike test, threshold run pace from a recent race, and lactate threshold heart rate from the last 20 minutes of a 30-minute time trial. Enter those four numbers at the top of this page and every zone is calculated for you.

What is Critical Swim Speed and how do I test it?

CSS is the swim equivalent of threshold pace - roughly what you could hold indefinitely. Swim a maximal 400 m, rest until fully recovered, then swim a maximal 200 m. CSS in seconds per 100 m is the 400 time minus the 200 time, divided by two. Both efforts have to be genuinely hard for the result to mean anything.

Should I use max heart rate or threshold heart rate for zones?

Threshold. Maximum heart rate barely changes with training, is unpleasant and slightly risky to measure properly, and produces zones that fit nobody in particular. Lactate threshold heart rate moves as you get fitter, comes out of any 30-minute time trial, and is what most modern zone systems are built on.

Why are my bike and run heart-rate zones different?

Because your threshold heart rate genuinely differs between them. Most athletes run at a higher heart rate than they ride, commonly by 5 to 10 beats, because more muscle mass is working against gravity. Using one set of zones for both means you will be training too hard in one discipline and too easy in the other.

How often should I retest?

Every six to eight weeks during a build, and after any block that changed your training substantially. A stale threshold quietly makes every prescribed session wrong in the same direction - too easy if you have improved, too hard if you have lost fitness or are carrying fatigue.

What is FTP and how do I test it without a lab?

Functional threshold power is roughly the power you could hold for an hour. The two practical tests are a ramp test, where software estimates it from the point you fail, and a 20-minute maximal effort where FTP is taken as 95% of your average power. The 20-minute version is more painful and more accurate; the ramp test is repeatable and good enough for setting zones.

Which zone should I do most of my training in?

Zone 2, by a wide margin. The most common error in age-group triathlon is turning easy sessions into moderate ones, which accumulates fatigue without delivering the adaptation that either easy or genuinely hard training would give. If your easy sessions feel like work, they are not easy sessions.

Free triathlon planning tool

Triathlon Training Zones

Swim, bike, run and heart-rate zones calculated from your own thresholds rather than from a formula based on your age. Enter four test results and every zone comes out in the units you actually train in.

Enter your four test results

Every zone below is derived from a threshold you can measure yourself. Nothing is stored or sent anywhere. If you have not tested one of them, the protocols are set out further down the page — they take a single session each.

Swim — CSS

400 m time200 m time

CSS 1:45 /100 m

Bike — FTP

FTP (watts)

From a ramp test, or 95% of a 20-minute best.

Run — threshold pace

Recent raceTime

Threshold 4:48 /km

Heart rate — LTHR

LTHR (bpm)

Average HR over the last 20 min of a 30-min time trial. Not max HR.

Your swim zones

From a Critical Swim Speed of 1:45 per 100 m. CSS is the swim equivalent of threshold: roughly the pace you could hold indefinitely.

Your swim zones
Zone	What it is for	Your target	Effort
Easy / technique	Drills, recovery, form work	1:55-2:01 /100 m	3-4/10
Endurance	The bulk of your swim volume	1:50-1:55 /100 m	5-6/10
Race pace (long course)	70.3 and Ironman swim effort	1:47-1:51 /100 m	6-7/10
Threshold / CSS	The main aerobic-speed session	1:43-1:47 /100 m	8/10
Speed	Short reps, sprint race pace	1:37-1:42 /100 m	9/10

CSS = (400 m time − 200 m time) ÷ 2, the standard two-distance estimate.

Your bike power zones

Coggan zones from an FTP of 210 W. An Ironman is raced in upper Z2 to low Z3; a 70.3 in Z3 to low Z4.

Your bike power zones
Zone	What it is for	Your target	Effort
Z1 Active recovery	Spin days, between intervals	63-116 W	2-3/10
Z2 Endurance	Long rides, most weekly volume	118-158 W	4-5/10
Z3 Tempo	Ironman race intensity sits here	160-189 W	6-7/10
Z4 Threshold	FTP work; 70.3 race intensity	191-221 W	8/10
Z5 VO2max	Short hard reps, sprint racing	223-252 W	9-10/10

Standard Coggan percentages of functional threshold power.

Your run pace zones

From a threshold pace of 4:48 per km, projected from the race you entered. Most weekly running belongs in Easy, which is usually slower than athletes expect.

Your run pace zones
Zone	What it is for	Your target	Effort
Easy	Recovery and most weekly volume	5:48-6:18 /km	3-4/10
Endurance	Long runs, Ironman marathon effort	5:28-5:48 /km	5-6/10
Steady / 70.3 pace	Half-distance race effort	5:08-5:28 /km	6-7/10
Tempo	Olympic-distance race effort	4:56-5:08 /km	7-8/10
Threshold	The key run session	4:45-4:53 /km	8-9/10
Interval	5k pace and faster, short reps	4:28-4:40 /km	9-10/10

Threshold projected with Riegel scaling to roughly a 10 km duration.

Your heart-rate zones

From a lactate threshold heart rate of 165 bpm. These are Friel-style LTHR zones, not percentages of max heart rate.

Your heart-rate zones
Zone	What it is for	Your target	Effort
Z1 Recovery	Easy spinning and recovery jogs	99-134 bpm	2-3/10
Z2 Aerobic	The bulk of endurance training	134-147 bpm	4-5/10
Z3 Tempo	Long-course race intensity	149-153 bpm	6-7/10
Z4 Threshold	Around LTHR; the key hard session	155-165 bpm	8/10
Z5 Above threshold	Short intervals only	165-175 bpm	9-10/10

Run LTHR is commonly 5-10 beats higher than bike LTHR, so test each discipline separately if you pace off heart rate on both.

Why age-based zones are the wrong tool

The most widely known zone formula is 220 minus your age, and it is close to useless for an individual. It was never derived as a training tool, the scatter around it is enormous, and two athletes of the same age can have maximum heart rates twenty beats apart. Building your training on it means every session is aimed at a person who does not exist.

Threshold-anchored zones fix this because a threshold is something you measure rather than assume. It also moves as you get fitter, which means your zones stay current instead of describing the athlete you were last winter.

The one genuine cost is that you have to test, and retest. That is four sessions to set up and one every couple of months to maintain — a small price for training that is actually aimed at you.

The four test protocols

One session each. Do them rested, in conditions you can repeat, and record the conditions along with the number — a CSS set swum in a crowded lane is not comparable with one swum in an empty pool.

The four test protocols
Threshold	Protocol	Time needed	How the number is derived
Swim (CSS)	400 m maximal, full recovery, then 200 m maximal	About 30 min including warm-up	CSS = (t400 − t200) ÷ 2, in seconds per 100 m
Bike (FTP)	20 min maximal after a proper warm-up, or a ramp test	45-60 min	FTP = 95% of 20-minute average power
Run (threshold pace)	A recent race, or a 30-minute solo time trial	Race, or 45 min	Threshold ≈ pace for roughly 10 km, or last-20-min TT pace
Heart rate (LTHR)	The same 30-minute time trial, running or riding	45 min	LTHR = average HR of the final 20 minutes

Test the bike and run thresholds on separate days. Doing both in one session gives you two numbers that are both wrong.

What race day asks of each zone

Race intensity by distance and discipline
Distance	Swim	Bike	Run
Sprint	At or just under CSS	Z4, ~88% FTP	Threshold to tempo
Olympic	Just under CSS	Z4 low, ~84% FTP	Tempo
70.3	CSS + 2-6 s/100 m	Z3 to low Z4, ~78% FTP	Steady
Ironman	CSS + 5-10 s/100 m	Upper Z2 to Z3, ~70% FTP	Endurance

Notice that the run column is expressed as an effort rather than a zone number. That is deliberate: the run happens after the bike, so the pace you can hold is lower than the same zone would suggest fresh. The run-off-the-bike calculator prices that difference.

Heart rate drifts, power does not

If you pace long races off heart rate, one thing will catch you out: cardiac drift. Over several hours your heart rate rises at a constant effort, driven by fluid loss and rising core temperature. Four hours into an Ironman bike leg, the number that meant Zone 2 in the morning means something harder.

The practical response is to treat heart rate as a ceiling rather than a target in long races, and to expect the ceiling to be met at a lower and lower power as the day goes on. Power does not drift, which is the strongest argument for a power meter on long course — and the reason the bike zones above are the ones to pace off if you have them.

Heat compounds it. A hot race raises heart rate at any given effort, so a plan built on cool-weather zones will have you riding too easy or running too hard, depending on which number you chase. The heat calculator adjusts the run side of that.

Frequently asked questions

How do I work out my triathlon training zones?: Test one threshold per discipline and derive everything from it: Critical Swim Speed from a 400 m and 200 m time trial, FTP from a ramp or 20-minute bike test, threshold run pace from a recent race, and lactate threshold heart rate from the last 20 minutes of a 30-minute time trial. Enter those four numbers at the top of this page and every zone is calculated for you.
What is Critical Swim Speed and how do I test it?: CSS is the swim equivalent of threshold pace - roughly what you could hold indefinitely. Swim a maximal 400 m, rest until fully recovered, then swim a maximal 200 m. CSS in seconds per 100 m is the 400 time minus the 200 time, divided by two. Both efforts have to be genuinely hard for the result to mean anything.
Should I use max heart rate or threshold heart rate for zones?: Threshold. Maximum heart rate barely changes with training, is unpleasant and slightly risky to measure properly, and produces zones that fit nobody in particular. Lactate threshold heart rate moves as you get fitter, comes out of any 30-minute time trial, and is what most modern zone systems are built on.
Why are my bike and run heart-rate zones different?: Because your threshold heart rate genuinely differs between them. Most athletes run at a higher heart rate than they ride, commonly by 5 to 10 beats, because more muscle mass is working against gravity. Using one set of zones for both means you will be training too hard in one discipline and too easy in the other.
How often should I retest?: Every six to eight weeks during a build, and after any block that changed your training substantially. A stale threshold quietly makes every prescribed session wrong in the same direction - too easy if you have improved, too hard if you have lost fitness or are carrying fatigue.
What is FTP and how do I test it without a lab?: Functional threshold power is roughly the power you could hold for an hour. The two practical tests are a ramp test, where software estimates it from the point you fail, and a 20-minute maximal effort where FTP is taken as 95% of your average power. The 20-minute version is more painful and more accurate; the ramp test is repeatable and good enough for setting zones.
Which zone should I do most of my training in?: Zone 2, by a wide margin. The most common error in age-group triathlon is turning easy sessions into moderate ones, which accumulates fatigue without delivering the adaptation that either easy or genuinely hard training would give. If your easy sessions feel like work, they are not easy sessions.

Put the zones to work

Free Triathlon Training Plans

Week-by-week plans whose sessions fill in with these zones.

Bike Split Calculator

Turn your FTP into a race bike split on a real course profile.

Swim Pace Calculator

Convert CSS into an open-water race swim split.

FTP Explained for Triathletes

What FTP is, why it matters, and how it controls your race.

Heart Rate vs Power vs Pace

Which metric to actually pace off on race day.

Zone 2 vs Zone 3 Training

Why most athletes train the middle and get the worst of both.

Guides that explain this calculator

FTP Explained for Triathletes: What It Is and Why It Controls Your Race

Master FTP for triathlon success. Learn what Functional Threshold Power means, how to test it, set training zones, and pace your Ironman bike leg.

Heart Rate vs Power vs Pace: What Should You Use in an Ironman?

Heart rate, power, or pace? Discover the science-backed framework for choosing the right pacing metric. Learn when to prioritize each in your Ironman.

Zone 2 vs Zone 3 Training: Why Most Athletes Fail the Ironman Marathon

Learn why Zone 3 overtraining hurts Ironman run performance, how Zone 2 builds durability, and how to apply the 80/20 rule.

Trust and methodology

How this page should be used

Model last reviewed

August 8, 2026

Maintained by

M Imtinan Farooq

Age-group triathlete and data engineer

Status

Planning estimate, not a race guarantee

Formula summary

Finish time = swim + T1 + bike + T2 + run, with related tools for risk checks.

Key assumptions

Entered paces, distances, transitions, and condition choices are race-realistic.

Limitations

Weather, course profile, water conditions, equipment, and execution can change results.

Sources

Full formulas, constants, and limitation notes are published on the methodology page. Use the official athlete guide for your own race when it comes to rules, cut-off times, venue policies, and safety instructions - those override anything here.