Kidney Stone Risk Calculator
Assess kidney stone risk from fluid intake, protein, sodium, and BMI.
Returns low, moderate, or high risk rating with dietary and hydration recommendations.
What Are Kidney Stones? Kidney stones (nephrolithiasis) are hard mineral deposits that form inside the kidneys when urine holds more crystal-forming substances than the fluid can dilute, mainly calcium, oxalate, and uric acid. They range from tiny specks to stones large enough to block urine flow, causing severe flank pain (renal colic), nausea, and blood in the urine.
About 1 in 10 people will develop a kidney stone during their lifetime. Men are more affected than women, though women’s rates have been rising.
Types of Kidney Stones
- Calcium oxalate (most common, ~80%), forms when calcium combines with oxalate in urine
- Uric acid: from high-protein diets or gout; more common in men
- Struvite: associated with urinary tract infections
- Cystine: rare; caused by a genetic disorder
Key Risk Factors
- Low fluid intake: the single most modifiable risk factor. Concentrated urine creates the perfect environment for stone formation. Aim for 2.5-3 liters of water daily, which is about 10-12 glasses.
- High sodium diet: increases calcium in urine by reducing kidney reabsorption
- High animal protein diet: increases uric acid and reduces citrate (a natural stone inhibitor)
- Obesity (high BMI): associated with more acidic urine and higher uric acid levels
- Prior kidney stones: 50% chance of recurrence within 5 years without preventive measures
- Family history: genetic factors account for a significant portion of risk
- Hot, dry climate: increases sweating and reduces urine output
How the score is built. Each factor below adds points, out of a maximum of 13:
| Factor | Points |
|---|---|
| Fewer than 6 glasses of water a day | 2 |
| 6 to 8 glasses (still below target) | 1 |
| More than 8 glasses | 0 |
| High sodium diet | 2 |
| High animal protein diet | 1 |
| BMI 25 to 29.9 | 1 |
| BMI 30 or above | 2 |
| Previous kidney stone | 3 |
| Family history | 2 |
| Hot or dry climate | 1 |
0 to 3 is low risk, 4 to 6 moderate, and 7 or more high.
A previous stone carries the heaviest weight for a reason. It is the strongest single predictor there is, stronger than any dietary factor, and it is why the advice for someone who has already passed one is different in kind, not just in degree, from the advice for everyone else.
Prevention Strategies
- Drink enough water to produce at least 2 liters of urine daily (urine should be pale yellow)
- Reduce sodium to under 2,300 mg/day
- Limit animal protein: moderate portions of meat, poultry, fish, and eggs
- Eat calcium-rich foods (do not avoid calcium: dietary calcium actually binds oxalate in the gut)
- Avoid high-oxalate foods if you have calcium oxalate stones (spinach, nuts, chocolate)
- Maintain a healthy weight through diet and exercise
- Speak to your doctor about potassium citrate supplementation if you have recurrent stones
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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