# URR Calculator (Urea Reduction Ratio)

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

> The urea reduction ratio calculator shows how much urea was removed during a haemodialysis session from the BUN before and after dialysis, and whether it meets the 65% minimum.

## Inputs

- Pre-dialysis BUN (mg/dL, mmol/L urea)
- Post-dialysis BUN (mg/dL, mmol/L urea)

## Results

- Urea reduction ratio
- Approximate Kt/V (no ultrafiltration)

## Formula

```
URR (%) = (pre-BUN − post-BUN) ÷ pre-BUN × 100
```

## Explanation

URR is the simplest measure of dialysis dose. It does not account for fluid removal or urea generation during dialysis, so Kt/V is more precise, but URR is widely used for monthly quality monitoring.

### How to use the URR Calculator

- **Pre-dialysis BUN**
- **Post-dialysis BUN**

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

### How it works

Enter BUN (or urea) before and after the dialysis session.

### Inputs explained

FieldWhat to enterPre-dialysis BUNUnits: mg/dL, mmol/L ureaPost-dialysis BUNUnits: mg/dL, mmol/L urea

### What each result means

- **Urea reduction ratio** = ([Pre-dialysis BUN] - [Post-dialysis BUN])÷[Pre-dialysis BUN]×100
- **Approximate Kt/V (no ultrafiltration)** = -ln([Post-dialysis BUN]÷[Pre-dialysis BUN])

### Example values

How the main result changes when **Pre-dialysis BUN** changes and everything else stays at the example values above:

Pre-dialysis BUN (mg/dL)Urea reduction ratio (%)3033455660677573907812083
*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 — Pre-dialysis BUN: 60 mg/dL; Post-dialysis BUN: 20 mg/dL.

Results — **Urea reduction ratio = 67 %**; Approximate Kt/V (no ultrafiltration) = 1.1.

## Key terms

- **URR**: Urea reduction ratio.

## FAQ

**What is a good URR?**
At least 65%, ideally 70% or more.

**How often is URR measured?**
Usually once a month.

**Why might URR be low?**
Short sessions, low blood flow, access recirculation or a clotted filter.


## Sources

- [National Kidney Foundation – Hemodialysis adequacy](https://www.kidney.org/atoz/content/hemodialysisdose)