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· 6 min read
3 eGFR Calculators, Compared Honestly
Heshan Fernando
Co-founder & COO
A blood test comes back with a creatinine value and, sometimes, an eGFR next to it. Sometimes the eGFR is missing entirely, and you are left with a number you cannot interpret until your next appointment.
Before going further: an eGFR is an estimate, and reading about it is not the same as being assessed. These tools exist to help you understand what a result means and what questions to ask, not to replace the clinician who ordered the test. With that said, the calculators differ in ways worth knowing — chiefly in which equation they use, because the same creatinine value produces different numbers depending on the formula.
How to judge an eGFR calculator
Which equation does it use? CKD-EPI 2021 is the current standard for adults and is race-free. Older equations like MDRD and Cockcroft-Gault are still around and give different results from the same inputs.
Is it race-free? The 2021 revision removed the race coefficient that earlier equations included. A calculator still asking for race is running an older formula.
Who is it built for? Some are clinical reference tools that assume you know how to interpret the output. Others are written for the person holding the test result.
Does it handle your units? Creatinine is reported in mg/dL in some countries and µmol/L in others, and entering one as the other produces a wildly wrong answer.
The comparison
| Tool | Best for | Free tier | Watch out |
|---|---|---|---|
| NIDDK eGFR Calculators | Authoritative, including paediatric | Free, US government resource | Written for health professionals, not patients |
| eGFR.app | Comparing equations against each other | Free, no account, no ads | 18 equations is overwhelming without background |
| eGFRCalculator.org | A single straightforward CKD-EPI 2021 result | Free, no registration | Doesn’t name which bodies recommend the equation |
Facts checked August 2026; tools change. Table covers only the 3 alternatives — our tool gets its own section below.
NIDDK eGFR Calculators
The most authoritative option, from the US National Institute of Diabetes and Digestive and Kidney Diseases. It offers three calculators: an adult one for ages 18 and over using the race-free CKD-EPI equations, and two paediatric calculators using the CKiD equations — the U25 for ages 1 to 25 and a bedside version for ages 1 to 16. An older race-based 2009 CKD-EPI calculator is kept available for reference during the transition.
It sits in the “for health professionals” section, and it reads that way: the page assumes clinical context rather than explaining it. NIDDK also recommends pairing eGFR with a urine albumin measurement, particularly near decision thresholds — a point most consumer calculators leave out entirely.
eGFR.app
The most complete, with 18 validated equations spanning 1976 to 2023 — EKFC, CKD-EPI in its 2021 and 2009 forms and variants, MDRD, Cockcroft-Gault, Schwartz Pediatric and CKiD U25 among them. It accepts creatinine in both mg/dL and µmol/L, and it gives CKD staging from G1 to G5, from “normal or high” at 90 and above down to kidney failure below 15. Free forever, no ads, no account.
It describes itself as being for clinical reference rather than long-form reading, and states plainly that eGFR is an estimate needing interpretation alongside history and clinical judgement. Eighteen equations is superb if you know why you would choose one; without that background it is mostly noise.
eGFRCalculator.org
The simplest of the three. It uses the CKD-EPI creatinine equation from 2021, takes serum creatinine (mg/dL or µmol/L), age and sex, and optionally accepts cystatin C, urine albumin-to-creatinine ratio and body surface area for a more precise result. 100% free, no registration.
It says the formula is recommended by major nephrology organisations without naming them, which is a small gap in an area where the provenance of the equation is the whole point. As a way of getting one modern number from one blood test, it does the job with no fuss.
GFR Reference Calculator
Ours is explicitly the educational one. It produces a kidney function estimate and runs entirely in your browser — nothing uploaded, no account, no external service contacted, which matters more than usual when the input is your own blood test result.
What it does not do: offer a library of equations to compare, handle paediatric cases, or serve as a clinical decision tool. If you are a clinician you want NIDDK or eGFR.app; if you are a patient trying to understand a number before an appointment, ours is written for you. It is worth knowing that freely available online GFR calculators vary in accuracy, which is one more reason to treat any of these as context rather than conclusion.
Which one to pick
- A clinician, or a paediatric case — NIDDK.
- Comparing what different equations give for the same value — eGFR.app.
- One modern number, minimum fuss — eGFRCalculator.org.
- Understanding what the number means before you ask about it — the tool below.
How to do it with GFR Reference Calculator
- Open the GFR Reference Calculator and enter the values from your blood test.
- Check the units on your report before entering creatinine — mg/dL and µmol/L are not interchangeable.
- Read the estimate as a range, not a precise figure.
- Take the result and your questions to the clinician who ordered the test.
The background reading is in how to read an eGFR result on a blood test. Other health tools are in the tools directory.
You might also need
The Creatinine Clearance Calculator covers the Cockcroft-Gault side of the same question, which still appears in medication dosing even where CKD-EPI is used for staging.
If your report includes a body surface area adjustment, the Body Surface Area Calculator explains where that figure comes from.
Frequently asked questions
Is there a free eGFR calculator that doesn’t need an account?
All four here are free without an account. NIDDK is the most authoritative, eGFR.app the most comprehensive, and ours the most explanatory for a non-clinical reader.
Why do two calculators give me different eGFR numbers?
Because they are running different equations. CKD-EPI 2021, MDRD and Cockcroft-Gault produce different estimates from identical inputs, and the older equations also included a race coefficient that current guidance has removed.
Does a single low eGFR mean I have kidney disease?
No. A single estimate is a snapshot, and it can move with hydration, recent exercise, some medications and lab variation. Chronic kidney disease is defined by findings persisting over months, alongside other measures such as urine albumin — which is a conversation for your clinician, not a calculator.
Final thought
Check which equation produced the number before comparing it to anything. A result from CKD-EPI 2021 and one from MDRD are not the same measurement, and the gap between them has sent plenty of people into an unnecessary weekend of worry.