Hydration & Sweat Loss Planner (+ Heat/Altitude Adjuster)

If you’re guessing your fluids, you’re winging performance and flirting with cramps or hyponatremia. This planner gives you sweat-rate based drink targets and sodium per liter with heat/altitude factors. Use Estimate (conditions) or Measured (scale method). Then get fluids/hour, session totals, per-15-min sips, and bottle mixes in plain English.

What you’ll get (fast)

• Sweat rate (L/h): estimated from temperature, humidity, intensity, sun exposure, altitude, acclimation—or computed from weigh-in/out.

• Drink rate target: ~60–90% of sweat rate, capped ≈1.0 L/h to reduce hyponatremia risk.

• Session fluids: total volume and per-15-min sip guidance.

• Electrolytes: sodium per liter (mg/L) from your test—or a pragmatic low/medium/high range—with table-salt equivalents and per-500 mL bottle mixes.

• Share/copy/print: keep it on your phone, hand it to a coach, or drop it into race notes.

How to use it (no fluff)

1. Pick Estimate or Measured.

   • Measured: use a scale. Formula: (pre − post + fluids − urine) ÷ duration (h).

2. Enter duration, session type, intensity, temperature, humidity, sun, altitude, acclimation.

3. Select sweat saltiness or enter tested sodium (mg/L).

4. Hit Build plan. You’ll see fluids/hour, session total, sodium/L, and exact bottle mixes.

What this tool won’t do

It won’t green-light chugging. Fluid caps exist for a reason: your gut has limits; your blood sodium does too. If your output says you “should” drink more than ~1.0 L/h, reality (and your stomach) disagree. Back off, cool the environment, or shorten the session.

Heat, altitude, and acclimation

Heat and altitude increase sweat rate for most people. Acclimated athletes often sweat more efficiently, but they still need sodium. The planner nudges numbers up or down and keeps the per-hour cap to avoid fantasy hydration.

Sodium: enough, not stupid

You don’t need a chemistry lab: aim for mg sodium per liter, not marketing copy. If you know your sweat sodium, enter it. If not, choose low/medium/high and the tool gives a sane range plus NaCl grams per liter (quick mixing at home, clear labels on bottles).

Sensible caveats

This is not medical advice. If you have kidney or heart conditions, take diuretics, or have a history of hyponatremia, talk to a clinician. Start conservative. Track body mass change, thirst, urine color, and how you feel post-session. Adjust like an adult.

Bottom line: hydrate to losses, cap intake, match sodium, and stop guessing.