Sick Day Fluid Intake Calculator
Calculate daily fluid needs when sick from body weight and fever severity.
Get hydration targets for illness broken down by drink type and hourly schedule.
When ill, the body loses fluids faster than normal through fever sweating, vomiting, diarrhea, and increased respiratory rate. This calculator estimates additional fluid replacement needed beyond baseline intake.
Baseline Daily Fluid Need:
Base Intake (mL) = Body Weight (kg) × 30–35 mL
Additional Fluid Loss Estimates:
- Fever: +150 mL per 1°C above 37°C (per hour of fever)
- Vomiting: +200 mL per episode
- Diarrhea: +200–400 mL per episode
- Increased respiration/sweating: +300–500 mL/day
Total Daily Fluid Goal (Sick):
Total = Baseline + Fever Loss + GI Loss + Sweat/Resp Loss
Worked Example — 70 kg adult with fever of 39.5°C, 3 vomiting episodes, 4 diarrhea episodes:
- Baseline: 70 × 32 = 2,240 mL
- Fever: (39.5 − 37) = 2.5°C × 150 mL × 12 hrs = 4,500 mL (fever losses total for the day)
(Simplified: add 10–15% fluid intake per degree of fever above 37°C)
- Vomiting: 3 × 200 = 600 mL
- Diarrhea: 4 × 300 = 1,200 mL
- Total goal: 2,240 + 600 + 1,200 = 4,040 mL/day (~4 liters)
Best Fluids When Sick:
- Oral rehydration solutions (ORS) — best for GI illness (electrolyte balance)
- Clear broths — sodium + warmth
- Diluted sports drinks — electrolytes without excess sugar
- Plain water — good but doesn’t replace electrolytes alone
Warning Signs Requiring Medical Attention: No urination for 8+ hours, sunken eyes, extreme dizziness, or inability to keep any fluids down for 12+ hours.