Weekly cold and heat, split by how cold the water was

Minutes of cold water is the number people most want and the number with the least behind it. Contrast shows it, splits it by temperature, and is specific about what the comparison it offers actually is.

What is counted

Every cold round — plunge or cold shower — and every hot round — sauna, hot bath or hot shower. The rings show this week; the chart shows the last twelve.

Cold minutes are then split by the plunge’s water temperature into four bands:

Showers appear in the weekly total and in none of the bands, because a shower produces no water reading. That is worth knowing before you look at a band chart that seems empty during a week of daily cold showers.

The reference point, and exactly what it is

A Danish study of eight experienced winter swimmers reported their routine: about 11 minutes of cold water and 57 minutes of sauna a week, over two or three visits, in water of about 1 to 9 °C.

That study was measuring brown fat and cold-induced thermogenesis in young healthy men. It found they burned more energy when cooled than men who did neither. What it was not doing was testing a dose — nobody assigned 11 minutes to one group and 22 to another.

So the figure on your screen is a description of what eight people happened to do, shown so you have something to place yourself against. The app’s own limits paragraph says the study was small, of young healthy men, and measured metabolism rather than long-term health.

It also names the gap that matters most: whether minutes of plunging do what hours of mild cold do in the brown fat studies has not been tested. Much of the cold-exposure literature involves long exposures to mildly cool air, which is a different stimulus from three minutes at 5 °C.

Why the split by temperature

Colder water is a stronger stimulus, and the research is specific about where the strength is.

The cold shock response — the gasp, the uncontrollable breathing, the heart rate spike — peaks in water between 10 and 15 °C and below. That is the band boundary the app uses, and it is why below-10 and 10-to-15 are separate rather than lumped as “cold”.

There are two consequences and they point in opposite directions. Colder water is more of whatever cold exposure is, and colder water is where the acute risk is concentrated. Both are true of the same band.

The honest state of the evidence

A 2025 meta-analysis across studies using water of 15 °C or colder found stress lower 12 hours after immersion and sleep quality improved, with a short-lived rise in inflammation. That is the strongest general statement available and it covers short-term outcomes in study participants.

Nothing ties a weekly cold total to long-term health the way the Finnish sauna cohorts tie weekly sauna minutes to cardiovascular outcomes. If you read a confident weekly cold prescription anywhere, it is an extrapolation, and usually from either the winter swimmer description above or from the cold shower trial.

This metric carries the borrowed tier for that reason. The measurement is sound; the reference it offers comes from research adjacent to the thing being measured.

Where the heat side is firmer

The 57 minutes of sauna in the same study is a much less interesting number than it looks, because the Finnish cohorts already give a better-grounded heat figure from a vastly larger sample.

The useful thing about the Danish figure is the ratio. Roughly five minutes of heat for every minute of cold is what that group did, which is a long way from how most people imagine a contrast session is balanced.

Reading your own twelve weeks

The twelve-week chart is where this section earns its place. A single week’s cold total is mostly noise — one missed session moves it 30%.

Two patterns show up often. The first is a cold total that holds steady while the band mix drifts warmer through spring, which is a fact about your water supply rather than your habit. The second is heat and cold moving independently: people who keep their sauna habit through a busy month and drop the plunge, because the plunge is the part that requires deciding.

Neither is visible in a weekly ring. Both are obvious across twelve weeks.

Safety, which belongs in this post more than most

Cold water is riskiest in the first minute. Very cold water can make it hard to move within about ten minutes, and your core temperature keeps falling for a while after you get out — the afterdrop. A weekly minutes figure says nothing about distribution, and twenty minutes taken as one immersion is a materially different proposition from four five-minute dips.

The app shows the total and does not suggest a way to reach it.