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Dehydration Risk Calculator

Determine your fluid deficit from daily intake and clinical symptoms — based on EFSA reference values and WHO/CDC dehydration signs.

Symptoms (check all that apply)

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Dehydration severity grades

SeverityDeficit (% body weight)Typical signs
No risk< 1 %None — normal fluid balance
Mild1–3 %Thirst, darker urine, mild fatigue
Moderate3–6 %Dry mouth, headache, dizziness, tachycardia
Severe> 6 %Confusion, no urination, low blood pressure, loss of consciousness

How it works

The calculator combines two methods: (1) Fluid balance — daily requirement equals 35 ml per kg of body weight (EFSA / IOM reference for healthy adults). Your current intake versus requirement yields the percentage deficit. (2) Clinical symptom score — adapted from WHO and CDC criteria, eight signs are weighted and summed. The final severity is the higher of the two estimates. Confusion is always treated as a red-flag, severe-grade symptom.

This calculator is intended for self-assessment in healthy adults and does not replace clinical evaluation. For infants, elderly patients, severe diarrhea, vomiting, heat stroke, confusion, or absent urination seek medical care immediately.

Frequently Asked Questions

When is someone considered dehydrated?+
Losing 1–2 % of body weight in fluid (about 0.7–1.4 kg in a 70 kg adult) counts as mild dehydration. From 5 % it is moderate, from 10 % severe and potentially life-threatening.
How much should I drink each day?+
EFSA recommends 2.0 L/day for women and 2.5 L/day for men from beverages — about 35 ml per kg of body weight. Heat, exercise, fever, or pregnancy add another 0.5–1.0 L.
Which symptoms suggest severe dehydration?+
Confusion, drowsiness, no urination for over 8 hours, sunken eyes, cool mottled skin, rapid weak pulse, low blood pressure. This is a medical emergency — call emergency services.
Do coffee and tea count toward fluid intake?+
Yes, in moderate amounts. The old idea that caffeine strongly dehydrates is debunked. Up to 400 mg caffeine per day (~4 cups of coffee) contributes net positively to fluid balance.
What is the fastest way to recover from mild dehydration?+
Sip water or an oral rehydration solution (such as ORS-200) — about 500 ml over 30 minutes. Drinking too fast can trigger hyponatremia, especially after long endurance exercise.
Are older adults at higher risk?+
Yes. Thirst sensation declines with age, kidneys concentrate urine less effectively, and medications (diuretics) increase losses. Older adults should drink regularly even without feeling thirsty.

Background

Dehydration Risk Calculator: Spot Fluid Loss with Symptoms

8 min