Body Weight (kg) Enter total body mass in kilograms (e.g., 70.5)

Sex Select sex Male Female Select biological sex for body water estimate

Current Serum Sodium (mmol/L) Enter measured sodium level in blood (e.g., 155)

Desired Serum Sodium (mmol/L) Enter target sodium level (e.g., 140)

Quick Examples:

Adult Male (Hypernatremia) Adult Female (Moderate)

Calculate Clear

This calculator is a screening tool only, not a diagnostic instrument. It is not intended to replace professional medical evaluation. Consult a healthcare provider.

What Is Water Deficit

Water deficit is the amount of water missing from your body. It usually happens when you lose more water than salt, causing sodium levels to rise. This calculation estimates the volume of free water you may need to help bring your sodium levels back to a safe range.

How Water Deficit Is Calculated

Formula

The formula first finds your total body water based on your weight and sex. Men typically have a higher water percentage than women. Then, it looks at how much higher your current sodium is compared to your goal. The larger the gap, the more water is needed to dilute the sodium to the desired level.

Why Water Deficit Matters

Understanding your water deficit is important for managing dehydration safely. It helps you see how much fluid might be involved in correcting sodium levels. This can guide better discussions with your doctor about hydration needs.

Why Safe Correction Is Important for Health

Adding water back too quickly can be dangerous for the brain. If sodium levels drop too fast, it may cause swelling. This calculator provides an estimate, but a doctor must plan the speed of correction to keep you safe.

For Biological Sex Differences

Men and women have different amounts of water in their bodies. Men generally have more total body water due to muscle mass. Because of this, the water deficit estimate for a man may be different than for a woman of the same weight.