# Sodium Change Calculator (Adrogué–Madias)

URL: https://speedycalculator.com/calculators/health/sodium-change/
Last updated: 2026-10-30

> The sodium change calculator predicts how much 1 litre of an intravenous fluid will change the serum sodium, using the Adrogué–Madias formula with total body water, to plan safe correction of hyponatraemia or hypernatraemia.

## Inputs

- Weight (kg, lb, st, g)
- Patient group (total body water)
- Serum sodium (mEq/L)
- Infusate
- Potassium added to infusate (mEq/L)

## Results

- Total body water
- Change in sodium per litre
- Litres to change sodium by 8 mEq/L

## Formula

```
TBW = weight × factor (0.6 men, 0.5 women, 0.5 older men, 0.45 older women, 0.6 children)
ΔNa per litre = (infusate Na + infusate K − serum Na) ÷ (TBW + 1)
```

## Explanation

Correcting sodium too fast is dangerous: rising too quickly in chronic hyponatraemia can cause osmotic demyelination, and falling too fast in hypernatraemia can cause brain swelling. The formula gives a starting estimate; sodium must be rechecked every few hours.

### How to use the Sodium Change Calculator

- **Weight**
- **Patient group (total body water)**
- **Serum sodium**
- **Infusate**
- **Potassium added to infusate**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter weight, patient group, current sodium and the fluid you plan to give.

### Inputs explained

FieldWhat to enterWeightUnits: kg, lb, st, gPatient group (total body water)Choose one: Adult man (60% of weight), Adult woman (50%), Older man (50%), Older woman (45%) …Serum sodiumIn mEq/LInfusateChoose one: 3% saline (513 mEq/L), 0.9% saline (154 mEq/L), Lactated Ringer's (130 mEq/L), 0.45% saline (77 mEq/L) …Potassium added to infusateIn mEq/L

### What each result means

- **Total body water** = [Weight]×[Patient group (total body water)]
- **Change in sodium per litre** = ([Infusate] + [Potassium added to infusate] - [Serum sodium])÷([Total body water] + 1)
- **Litres to change sodium by 8 mEq/L** = abs(8÷[Change in sodium per litre])

### Example values

How the main result changes when **Weight** changes and everything else stays at the example values above:

Weight (kg)Change in sodium per litre (mEq/L)3517.952.512.1709.187.57.31056.11404.6
*Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.*

## Worked example

Inputs — Weight: 70 kg; Patient group (total body water): Adult man (60% of weight); Serum sodium: 120 mEq/L; Infusate: 3% saline (513 mEq/L); Potassium added to infusate: 0 mEq/L.

Results — Total body water = 42 L; **Change in sodium per litre = 9.1 mEq/L**; Litres to change sodium by 8 mEq/L = 0.88 L.

## Key terms

- **TBW**: Total body water.
- **ODS**: Osmotic demyelination syndrome.

## FAQ

**What is a safe correction rate?**
In chronic hyponatraemia, no more than 8–10 mEq/L in 24 hours (8 in high-risk patients).

**Why add potassium?**
Potassium also raises sodium because it moves into cells in exchange.

**Is the formula exact?**
No – ongoing losses and urine output change sodium too; measure frequently.


## Sources

- [Adrogué HJ, Madias NE. Hyponatremia. N Engl J Med, 2000](https://pubmed.ncbi.nlm.nih.gov/10816188/)