Interval Training Zones Calculator

Calculator Inputs

Enter your values, choose a method, then submit to generate zones and a session plan.

Age

Used for estimating max heart rate in auto mode.

Sex (optional)

Kept optional because formulas vary across sources.

Resting Heart Rate (bpm)

Best measured upon waking for 3–5 days.

Max Heart Rate Mode

Use manual only if tested or well-estimated.

Auto Formula

Pick one estimate and keep it consistent.

Zone Method

HRR often personalizes zones better.

Zone System

More zones = finer control for advanced training.

Interval Focus

This sets the default target zone and structure.

Session Builder

Switch to custom to control work/rest/rounds.

Work Duration (seconds)

Used when you select “Use my durations”.

Rest Duration (seconds)

Rest between repeats (last rest excluded).

Rounds

Total repeats of work segments.

Warm-up (minutes)

Typically in Z1–Z2.

Cooldown (minutes)

Easy pace until breathing normalizes.

Cycling FTP (optional, watts)

Adds power zones for bike training.

Running Threshold Pace (optional)

Accepts mm:ss or decimal minutes.

Pace Unit

Used only when threshold pace is provided.

Reset

Example Data Table

Sample inputs and typical outputs for quick reference.

Age	Resting HR	Method	System	Example Z4 Range	Example Z5 Range	Session Focus
30	60 bpm	Karvonen HRR	5 zones	162–174 bpm	174–187 bpm	VO2max Intervals
40	65 bpm	%HRmax	5 zones	144–162 bpm	162–180 bpm	Threshold Blocks

Formula Used

Max Heart Rate (auto): choose one estimate, such as 220 − age or 208 − 0.7×age.
Percent of Max: TargetHR = HRmax × intensity.
Karvonen HRR: TargetHR = HRrest + (HRmax − HRrest) × intensity.
Power Zones (optional): TargetW = FTP × intensity.
Pace Zones (optional): TargetPace = ThresholdPace × factor (smaller is faster).

How to Use This Calculator

Enter your age and resting heart rate.
Select auto estimation or enter a tested max heart rate.
Pick a method (HRR or %HRmax) and a zone system.
Choose an interval focus, then submit to view zones.
Use the session plan to structure your workout.
Download CSV or PDF to save your report.

FAQs

1) Which is better: HRR or %HRmax?

HRR includes resting heart rate, so it often matches your fitness changes better. %HRmax is simpler and works fine when resting heart rate is unknown or unstable.

2) How do I measure resting heart rate accurately?

Measure right after waking, before caffeine or phone scrolling. Record 3–5 mornings and use the average. A chest strap or validated watch improves accuracy.

3) Is age-based max heart rate accurate?

It’s a population estimate, not a personal test. Many people differ by 10–20 bpm. If you have a recent hard effort value, manual entry can be closer.

4) Why do interval targets feel hard to reach?

Heart rate lags behind effort, especially for short sprints. Use perceived effort and breathing early, then let heart rate rise during later repeats. Power or pace can be more responsive.

5) What if my heart rate drifts upward?

Drift is common with heat, dehydration, or fatigue. Reduce intensity slightly, extend recovery, or shorten total volume. Track conditions and compare similar workouts over time.

6) How should I choose a zone system?

Use 3 zones for simplicity, 5 zones for most athletes, and 7 zones when you want fine control for threshold and high-intensity work. Consistency matters more than the exact model.

7) How do FTP power zones help?

Power responds instantly, so it’s great for intervals. If you know your FTP, the added power zones can guide work segments while heart rate catches up.

8) Can I use threshold pace for running workouts?

Yes. Enter your threshold pace to get pace ranges for easy, tempo, and interval efforts. Use pace on flat terrain and adjust for hills, wind, or surface changes.