KelvinKelvin · cold plunge tools
Cold plunge calculator: how long to stay in a cold plunge at your water temperature
Enter your cold plunge temperature or ice bath temperature in °F or °C. You get a safe starting time, a four-week ramp and the point where afterdrop starts to matter, worked out from the same safety numbers the Kelvin app uses. Guidance, not medical advice.
Cold-shock water (59 °F / 15 °C or colder): the first 30 seconds trigger a gasp reflex. Exhale slowly and stay in control before you settle in.
Your four-week ramp
| Week | In the water | Warm-up after | Note |
|---|---|---|---|
| Week 1 | 1:30 | 6:00 | Ride out the first 30 seconds |
| Week 2 | 2:00 | 6:00 | Afterdrop line: warm up slowly |
| Week 3 | 2:30 | 7:00 | Afterdrop line: warm up slowly |
| Week 4 | 3:00 | 7:00 | Afterdrop line: warm up slowly |
- Mind the afterdrop: your core keeps cooling after you get out. Layer up and warm slowly, no scalding shower.
- Ride out the cold shock: the first 30 seconds trigger a gasp reflex. Exhale slowly before you settle in.
- Never hold your breath in or near the water. Breath-holds right before or during a plunge can cause shallow-water blackout and drowning. Do all breathwork on dry land.
- Heart condition, high blood pressure or pregnancy? Cold exposure stresses the heart and circulation: talk to a doctor before plunging.
How long to stay in a cold plunge, by temperature
Cold exposure behaves like a dose: how cold the water is, multiplied by how long you stay in. Kelvin measures it the same way, as minutes times degrees below 20 °C (68 °F). The calculator keeps that dose steady, so colder water gets a shorter session and cooler water a longer one.
- Starting time: the dose of Kelvin's Beginner ramp (a 1:00 plunge) in 39 °F (4 °C) water, the temperature the app plans for, converted to your water. Never under 0:30, never over 3:00.
- Weekly step: about 30 seconds a week, the step Kelvin's coach digest suggests.
- Longest at this temperature: the dose of Kelvin's longest protocol (Athletic recovery, 3:00) at the edge of extreme cold, 37 °F (3 °C), and never past 5:00, where the app warns that a plunge is too long.
- Afterdrop line: from 2:00 in the water the app warns about afterdrop. The warm-up times are the app's own protocol warm-ups, 4 to 7 minutes.
Worked examples
| Ice bath temperature | Week 1 | Week 4 | Longest |
|---|---|---|---|
| 59 °F (15 °C) | 3:00 | 4:30 | 5:00 |
| 55 °F (12.8 °C) | 2:00 | 3:30 | 5:00 |
| 50 °F (10 °C) | 1:30 | 3:00 | 5:00 |
| 46 °F (7.8 °C) | 1:15 | 2:45 | 4:00 |
| 41 °F (5 °C) | 1:00 | 2:30 | 3:15 |
| 37 °F (2.8 °C) | 0:45 | 2:15 | 2:45 |
| 32 °F (0 °C) | 0:45 | 2:15 | 2:30 |
See every temperature and time at once on the cold plunge temperature chart.
Not medical advice. This calculator is general guidance from a tracking app, not a doctor. Cold water causes cold shock and afterdrop, and can cause hypothermia.
Check with a doctor first if you have a heart condition, high blood pressure, are pregnant, have a history of fainting or seizures, or have Raynaud's or cold urticaria.
Never hold your breath in or near the water. Breathwork belongs on dry land. Never plunge alone in very cold or open water, and know how you will get out before you get in.
Questions
How long should you stay in a cold plunge?
It depends on the water temperature. At 50 °F (10 °C) the calculator starts you at 1:30 and steps to 3:00 over four weeks; at 39 °F (4 °C) it starts at 1:00; at 32 °F (0 °C) it starts at 0:45 and never goes past 2:30. No session passes 5:00, the point at which the Kelvin app warns that a plunge is too long.
What is a good cold plunge temperature for beginners?
Start warmer than you think: 50–59 °F (10–15 °C) gives a real cold-shock response with time to learn to breathe through it. Water at 37 °F (3 °C) or colder is for the well-adapted only, never alone.
What is the afterdrop line?
Your core keeps cooling for a while after you get out. Kelvin treats any plunge of 2:00 or longer as carrying meaningful afterdrop risk: dry off, layer up and warm up slowly, and skip the scalding shower.
Where do these numbers come from?
From the Kelvin app's own safety engine: cold shock at 15 °C (59 °F) or colder, extremely cold at 3 °C (37.4 °F) or colder, afterdrop from 2:00, too long past 5:00, and a dose of minutes times degrees below 20 °C. The page runs the same code, checked against the app's outputs. It is guidance, not medical advice.
Who should not cold plunge?
Talk to a doctor first if you have a heart condition or high blood pressure, are pregnant, have a history of fainting or seizures, or have Raynaud's or cold urticaria. Never hold your breath in or near the water.
Related
- Cold plunge temperature chart
- How long to stay in a cold plunge
- What temperature should a cold plunge be?
- Cold plunging for beginners
Time it and log it in Kelvin
Kelvin is a free cold plunge timer and ice bath tracker: breath-up, a plunge countdown with a first-30-second cold-shock coach, and a guided warm-up. Log the water temperature in °F or °C and watch your streak and total time in the cold grow. No hardware, no account; your log stays on your phone.