Sweat is mostly water plus sodium, with smaller amounts of potassium and magnesium. How much you need to replace depends on what you are doing and how hard you sweat. Answer three questions below for a practical ballpark, then see the reference table for what each electrolyte actually does.
Electrolyte Calculator
Sweat is mostly water plus sodium, with smaller amounts of potassium and magnesium. How much you need to replace depends on what you are doing and how hard you sweat. Answer three questions below for a practical ballpark, then see the reference table for what each electrolyte actually does.
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Electrolyte calculator: what to replace after sweating
Sauna, cold plunge, training or keto — answer three quick questions and get a sodium ballpark, timing and what else to add.
General sports-science guidance based on typical sweat losses, not medical advice. If you have blood pressure or kidney issues, talk to a doctor before adding sodium.
The 4 electrolytes: what they do and where to get them (2026)
| Electrolyte | Daily need (adults) | What it does | Best food sources | When to supplement |
|---|---|---|---|---|
| Sodium | 1,500–2,300 mg (more if sweating hard) | Fluid balance, nerve signals, blood pressure | Salt, broth, pickles | Heavy sweating, sauna, keto/fasting |
| Potassium | 2,600–3,400 mg | Blood pressure, muscle contraction | Potatoes, bananas, beans, yogurt | Rarely — food first; low-carb diets |
| Magnesium | 310–420 mg | 300+ enzyme reactions, muscle relaxation, sleep | Pumpkin seeds, almonds, spinach, dark chocolate | Common shortfall — see our magnesium calculator |
| Chloride | Paired with sodium | Fluid balance, stomach acid | Salt (sodium chloride) | Covered whenever you replace sodium |
Electrolytes and heat: the sauna case
A 20–40 minute sauna session can pull half a liter to a liter of sweat out of you. That is mostly water, but also a few hundred milligrams of sodium. Replacing fluid without any sodium after frequent sessions can leave you flat, headachy or crampy — the classic “sauna hangover”. Water plus a pinch of salt (or an unsweetened electrolyte mix) after each full session prevents it. Cold plunging, by contrast, causes minimal sweat loss — hydration matters, electrolyte replacement usually does not.
Electrolyte FAQ
What electrolytes do you actually need?
Four: sodium (the big one when you sweat), potassium, magnesium and chloride. Sodium is the only one most people need to actively replace around sweating; potassium and magnesium are better covered by food and, in magnesium’s case, a targeted supplement if you run low.
When should I take an electrolyte supplement?
When you sweat hard for over an hour, after long or hot sauna sessions, during keto or fasting (low insulin flushes sodium), or after illness with fluid loss. If none of those apply, your diet almost certainly covers you.
Are sports drinks the same as electrolyte supplements?
No. Most sports drinks are mainly sugar with a token 100–200 mg of sodium. Dedicated electrolyte mixes deliver therapeutic sodium (500–1,000 mg) with sensible potassium and magnesium and little or no sugar.
Do you lose electrolytes in a cold plunge?
Barely. Cold water immersion causes very little sweating, so there is nothing meaningful to replace. If you do contrast therapy (sauna + cold), follow the sauna guidance: fluid plus sodium after the heat rounds.
Values based on NIH dietary reference intakes and sports-science sweat studies. General education, not medical advice.
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