Heart Rate Reserve Calculator
Karvonen target from max, resting, and intensity percent.
What it does
Karvonen personalizes zones with resting rate. Two runners with max 180 differ if one rests at 50 and the other at 70. Reserve, max minus rest, captures that gap.
The tool above takes max, resting, and intensity percent and returns target, reserve, and zone. The defaults 180, 60, and 70 match the worked example, so the page opens showing 144 bpm.
Target is reserve times intensity over 100 plus resting. Here reserve 120 times 0.7 is 84, plus 60 is 144. Zones read under 50 light, 50 to 70 moderate, over 70 vigorous.
Use this to set steady runs, not max sprints. Medicines, heat, and altitude shift heart rates. Stop with chest pain or dizziness and seek care.
This page shows the formula, one full hand checked example at 180/60/70, a reference table, and practice checks that run through the tool.
How to use
- Type max heart rate in bpm.
- Type resting morning rate in bpm.
- Type intensity percent.
- Read Target as beats per minute.
- Read Reserve as max minus rest.
- Train in zone with easy days light.
Formula
- max
- Maximum bpm.
- rest
- Resting bpm.
- pct
- Intensity percent.
Resting must sit below max. Estimates only, not medical advice.
Worked example
Example: max 180, rest 60, 70 percent
Runner max 180 with rest 60 trains at 70 percent. Find target.
- Reserve: 180 minus 60 = 120 bpm.
- Share: 120 x 70 / 100 = 84.
- Target: 84 + 60 = 144 bpm.
- Zone: 70 sits at top of Moderate.
- Check: 144 between rest 60 and max 180.
- Easy days drop toward 50 percent.
Reference table
| Intensity | Target | Zone |
|---|---|---|
| 50 % | 120 bpm | Moderate |
| 60 % | 132 bpm | Moderate |
| 70 % | 144 bpm | Moderate |
| 85 % | 162 bpm | Vigorous |
Limits
- Estimates only. Not medical advice.
- Max often estimated, not measured.
- Medicines and heat shift rates.
- Stop with warning symptoms.
Common mistakes
- Using 220 minus age max as measured.
- Swapping max with resting.
- Reading percent of max instead of reserve.
- Training hard daily without light days.
- Ignoring medicines that blunt rate.
Try it yourself
Quick checks. Answers sit tucked under each question.
Max 190, rest 55, 60 percent?
Reserve 135 bpm, target 136 bpm, Moderate.
Max 180, rest 60, 50 percent?
Reserve 120 bpm, target 120 bpm.
Questions
180/60 at 70?
144 bpm.
Reserve?
Max minus rest.
Zones?
Under 50 light, 50-70 moderate, over 70 vigorous here.
Max measured?
Best by test. Estimates err.
Rest?
Morning resting before rising.
Medical?
No. Info only.