GFR Calculator

Introduction

The GFR Calculator helps you estimate your glomerular filtration rate, which is a number that shows how well your kidneys are working. GFR stands for Glomerular Filtration Rate, and it measures how much blood your kidneys filter each minute. Doctors use this number to check for kidney disease and to see what stage it might be in. A normal GFR is usually 90 or above, while a lower number may mean your kidneys are not filtering as well as they should. This tool uses factors like your age, sex, and creatinine level to give you a quick estimate. Keep in mind that this calculator is for informational purposes only and should not replace advice from your doctor.

How to Use Our GFR Calculator

Enter a few details about yourself below to estimate your glomerular filtration rate (GFR). This number tells you how well your kidneys are filtering waste from your blood. A higher GFR means healthier kidneys.

Serum Creatinine: Enter your serum creatinine level in mg/dL. This is a waste product found in your blood. Your doctor can get this number from a simple blood test. Higher creatinine levels may mean your kidneys are not working as well as they should.

Age: Enter your age in years. GFR naturally goes down as you get older, so age plays a big role in the calculation. If you're unsure of your exact age, you can use our Age Calculator to determine it precisely.

Sex: Select your biological sex. Males and females produce different amounts of creatinine, which affects the GFR result.

Race: Select your race if the option is provided. Some GFR formulas use race as a factor, though newer equations like the 2021 CKD-EPI formula have removed this variable for a more fair and accurate result.

After you fill in all the fields, the calculator will show your estimated GFR in mL/min/1.73 m². A normal GFR is 90 or above. A GFR below 60 for three months or more may point to chronic kidney disease. Always share your results with your doctor for a proper diagnosis.

What is GFR?

GFR stands for Glomerular Filtration Rate. It is the best way to measure how well your kidneys are working. Your kidneys filter waste and extra water from your blood to make urine. GFR tells you how much blood your kidneys clean each minute. It is measured in milliliters per minute (mL/min).

Why Does GFR Matter?

Your GFR number helps doctors figure out if your kidneys are healthy or damaged. A normal GFR is around 90 or higher. If your GFR drops below 60 for three months or more, it usually means you have chronic kidney disease (CKD). The lower your GFR, the more damage your kidneys have. A GFR below 15 means the kidneys are very close to failure or have already failed.

GFR and Kidney Disease Stages

• Stage 1: GFR 90 or above — Kidney damage with normal function
• Stage 2: GFR 60 to 89 — Mild loss of function
• Stage 3a: GFR 45 to 59 — Mild to moderate loss
• Stage 3b: GFR 30 to 44 — Moderate to severe loss
• Stage 4: GFR 15 to 29 — Severe loss of function
• Stage 5: GFR below 15 — Kidney failure

How is GFR Calculated?

Doctors estimate GFR using a blood test called serum creatinine. Creatinine is a waste product made by your muscles. Healthy kidneys remove it from your blood. When kidneys are damaged, creatinine builds up. The most common formula used is the CKD-EPI equation, which factors in your creatinine level, age, sex, and sometimes race to give an estimated GFR (eGFR). Understanding your body composition can also provide context for your creatinine levels — tools like our Body Fat Calculator or Lean Body Weight Calculator can help you assess your muscle mass, which directly influences creatinine production. Additionally, your BSA Calculator can determine your body surface area, which is the unit GFR is normalized to (1.73 m²).

What Can Affect Your GFR?

Several things can change your GFR reading. Age is a big factor — GFR naturally goes down as you get older. Dehydration, certain medications, high blood pressure, and diabetes can also lower your GFR. Eating a lot of protein or having more muscle mass can raise creatinine levels, which may affect the estimate. That is why doctors look at GFR over time, not just one test. Tracking your daily water intake can help you stay properly hydrated and support kidney function. If you're managing your diet to protect your kidneys, our Protein Calculator can help you determine the right amount of protein, as excess protein intake can burden the kidneys. You may also find our Macro Calculator useful for balancing your overall nutrition.

How to Protect Your Kidneys

You can help keep your GFR healthy by drinking enough water, eating a balanced diet low in salt, staying active, and managing conditions like diabetes and high blood pressure. Monitoring your overall health metrics is important — our Calorie Calculator and BMR Calculator can help you maintain a healthy weight, which reduces strain on your kidneys. Keeping track of your waist-to-hip ratio and waist-to-height ratio can also help you identify obesity-related risks that contribute to kidney disease. Tools like our Ideal Body Weight Calculator and TDEE Calculator can support your overall wellness goals. Avoid overusing pain medications like ibuprofen, which can harm the kidneys. Regular checkups and blood tests are the best way to catch kidney problems early, when they are easier to treat. For those managing their cardiovascular health alongside kidney health, our Heart Rate Zone Calculator and VO2 Max Calculator can help you exercise safely and effectively.

Frequently Asked Questions

What is a good GFR number?

A good GFR is 90 or above. This means your kidneys are filtering blood at a normal rate. A GFR between 60 and 89 shows a mild decrease. If your GFR stays below 60 for three months or more, it may mean you have chronic kidney disease. Talk to your doctor about what your number means for you.

What is serum creatinine and how do I get it?

Serum creatinine is a waste product your muscles make. Your kidneys remove it from your blood. A simple blood test at your doctor's office will give you this number. Normal levels are about 0.7 to 1.3 mg/dL for adults. Higher levels may mean your kidneys are not filtering well.

What is the difference between eGFR and measured GFR?

eGFR stands for estimated GFR. It is calculated from a blood test using a math formula. Measured GFR is done by injecting a special substance into your blood and tracking how fast your kidneys clear it. Measured GFR is more accurate but takes more time and costs more. Most doctors use eGFR for routine screening.

Which equation should I choose on this calculator?

For most adults, choose CKD-EPI Creatinine (2021). It is the current standard and does not use race. If your doctor has ordered a Cystatin C blood test, you can use the Cystatin C or combined equation for a more precise result. The MDRD equation is older and less commonly used today.

What is Cystatin C?

Cystatin C is a protein made by all the cells in your body. Like creatinine, your kidneys filter it from your blood. A Cystatin C blood test can give a more accurate eGFR, especially for people with unusual muscle mass. Normal Cystatin C levels are about 0.6 to 1.0 mg/L. Not all labs test for it, so ask your doctor if it is available.

Why did the 2021 CKD-EPI equation remove race?

The older equations used a race factor that could lead to unfair differences in care. In 2021, the NKF-ASN Task Force recommended removing race from the GFR formula. The new CKD-EPI 2021 equation gives the same result for everyone regardless of race, which helps ensure equal treatment for all patients.

Can I use this calculator for children?

Yes. Click the Pediatric GFR tab at the top of the calculator. It uses the Bedside Schwartz equation, which is designed for children aged 1 to 17. You will need the child's height and serum creatinine level. Adult equations are not accurate for children.

What does mL/min/1.73 m² mean?

This is the unit used for GFR. It means milliliters of blood filtered per minute, adjusted to a standard body surface area of 1.73 square meters. This adjustment lets doctors compare results between people of different body sizes.

Can GFR change from day to day?

Yes. Your GFR can change based on how much water you drink, what you eat, your medications, and whether you are sick. A single test may not show the full picture. That is why doctors usually check your GFR more than once over several months before diagnosing kidney disease.

How do I switch creatinine units between mg/dL and µmol/L?

Click the unit button next to the creatinine input field. It will toggle between mg/dL and µmol/L and automatically convert your entered value. Labs in the United States typically use mg/dL, while many other countries use µmol/L.

What if my GFR is below 15?

A GFR below 15 is classified as Stage 5 kidney disease, also called kidney failure. At this stage, the kidneys can no longer keep you healthy on their own. Treatment usually involves dialysis or a kidney transplant. See a kidney doctor (nephrologist) right away if your GFR is this low.

Is eGFR accurate for everyone?

No. eGFR may be less accurate for people with very high or low muscle mass, pregnant women, people with acute kidney injury, amputees, or those on unusual diets. In these cases, a doctor may order a measured GFR or use a Cystatin C-based equation for a better estimate.

How often should I check my GFR?

If you are healthy, a GFR check during your yearly physical is usually enough. If you have diabetes, high blood pressure, or known kidney disease, your doctor may want to check it every 3 to 6 months. People with Stage 4 or 5 kidney disease may need monthly monitoring.

Does a high creatinine always mean bad kidneys?

Not always. People with more muscle mass naturally produce more creatinine, which can raise their level without any kidney damage. Eating a large amount of cooked meat before the test can also raise creatinine temporarily. Your doctor will look at the full picture, not just one number.

What is the Bedside Schwartz equation?

The Bedside Schwartz equation estimates GFR in children aged 1 to 17. It uses the child's height in centimeters and serum creatinine level. The formula is: eGFR = 0.413 × height (cm) ÷ serum creatinine (mg/dL). It is simpler and more appropriate for kids than adult equations.