Dietary Acid Load (PRAL) Calculator

Understanding the PRAL (dietary acid load) calculator — concept and principle

PRAL, the potential renal acid load, estimates how much acid or base your diet leaves for the kidneys to excrete each day. You enter daily intakes of protein, phosphorus, potassium, magnesium and calcium, and the calculator returns PRAL in milliequivalents per day (mEq/day) and labels the diet as acid-forming or base-forming. Researchers use it to study diet, bone health, kidney stones and kidney disease.

The acid side outweighs the base side by 9.62 mEq a day in the default diet.

How it is calculated

PRAL (mEq/day) = 0.4888 × protein (g) + 0.0366 × phosphorus (mg) − 0.0205 × potassium (mg) − 0.0125 × calcium (mg) − 0.0263 × magnesium (mg)

Protein and phosphorus raise PRAL (acid side); potassium, calcium and magnesium lower it (base side). A positive result is acid-forming, a negative result is base-forming. Use daily totals: protein in grams, minerals in milligrams.

The principle

Remer and Manz built PRAL from the main ions that create or neutralise acid after digestion. Protein contains sulfur amino acids (methionine and cysteine) that are metabolised to sulfuric acid, and phosphorus contributes phosphate. Potassium, magnesium and calcium in foods such as fruit and vegetables usually come with organic anions (for example citrate) that are metabolised to bicarbonate, a base. Each coefficient combines the ion's charge, molar mass and average intestinal absorption. The model was validated against measured urinary net acid excretion in healthy adults.

Worked example

Inputs: protein 90 g, phosphorus 1,300 mg, potassium 3,000 mg, magnesium 350 mg, calcium 900 mg.
Acid terms: 0.4888 × 90 = 43.99; 0.0366 × 1,300 = 47.58. Sum = 91.57.
Base terms: 0.0205 × 3,000 = 61.50; 0.0125 × 900 = 11.25; 0.0263 × 350 = 9.21. Sum = 81.96.
PRAL = 91.57 − 81.96 = 9.62 mEq/day, a positive value, so the diet is classed as acid-forming.

Each point is the calculator re-run with only “Potassium (mg)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Potassium (mg)	PRAL (mEq/day)
750	55.74
1,500	40.37
2,250	24.99
3,000	9.62
3,750	-5.76
4,500	-21.13
6,000	-51.88

How to read the result

Where does your result fall?

Values near zero mean acid and base sources roughly balance. Diets heavy in meat, cheese and grains and low in produce give positive values; plant-heavy diets often fall below zero. The number is not your blood pH: healthy kidneys and lungs keep blood pH in a tight range whatever you eat. PRAL is most useful for comparing your own diet before and after a change.

Common mistakes

Entering phosphorus or potassium in grams instead of milligrams, which shifts the result by a factor of 1,000.
Reading a positive PRAL as a sign of disease or of acidic blood.

Keep in mind: PRAL is a research estimate based on average absorption, not a measure of your body's acid balance or a diagnosis. People with kidney disease should not change protein, potassium or phosphorus intake without their doctor or dietitian, because these nutrients may need strict limits.

Frequently asked questions

Are foods that taste sour, like lemons, acid-forming?

No. Lemons are rich in potassium and citrate, which are metabolised to base, so their PRAL is negative despite the sour taste.

Is a lower PRAL always better?

Not necessarily. A very negative score can come from too little protein; overall diet quality matters more.

Sources: Remer T, Manz F. Potential renal acid load of foods and its influence on urine pH. J Am Diet Assoc 1995;95(7):791–797.

Checked 8 Nov 2026. Remer & Manz, J Am Diet Assoc 1995.

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