eGFR Calculator (CKD-EPI 2021)
Renal function
What is the patient’s eGFR?
Calculate adult CKD-EPI 2021 eGFR from serum creatinine. Add cystatin C for the combined 2021 estimate and BSA when an absolute mL/min value is needed.
Serum creatinine unit
Select the exact unit printed on the laboratory report before entering the value.
Enter the measured serum creatinine in the selected unit.
This adult CKD-EPI calculator accepts ages 18 years and older.
Sex used by the equation
The CKD-EPI 2021 equations use sex-specific constants. Select the equation term required for the calculation you are performing.
Transgender, nonbinary or intersex patients
Pregnancy limitation
Use stable laboratory markers
Simple answer
2021 CKD-EPI creatinine formula
The default result is the adult 2021 CKD-EPI creatinine eGFR.
Serum creatinine is converted to mg/dL internally when µmol/L is entered. The result is indexed to 1.73 m².
If cystatin C is available
MedMaths can also calculate the separate 2021 CKD-EPI creatinine-cystatin C equation. NIDDK describes the combined estimate as generally more accurate than creatinine alone when both standardized markers are available, particularly near important decision thresholds. Non-GFR determinants can still make a single-marker equation or measured GFR more appropriate in selected patients.
eGFRcr-cys = 135 × min(SCr/κ,1)^α × max(SCr/κ,1)^−0.544 × min(Scys/0.8,1)^−0.323 × max(Scys/0.8,1)^−0.778 × 0.9961^Age [× 0.963 if female]
What does the result mean?
The main result is an indexed estimate of GFR in mL/min/1.73 m². MedMaths also shows the matching G category, but that category alone is not a CKD diagnosis.
Need an absolute mL/min value?
Add patient BSA and MedMaths will de-index the eGFR using eGFR × BSA ÷ 1.73. G-category interpretation still uses the indexed result. If BSA has not yet been calculated, use the BSA Calculator first.
Medication dosing guidance is changing
In 2026, the National Kidney Foundation and major U.S. pharmacy organisations endorsed transition toward race-free 2021 CKD-EPI eGFR, with BSA adjustment when appropriate, for medication-related decisions. Some medicine labels and specialty protocols still specify Cockcroft-Gault or another equation. Follow the method named by the governing source.
If the governing source explicitly names Cockcroft-Gault CrCl, use the Creatinine Clearance Calculator instead. For the deeper comparison, see the eGFR vs CrCl guide.
Clinical use and safety
When to use this calculator — and its limits
The arithmetic can be correct while the clinical decision is still wrong. These boundaries show what the calculator can and cannot establish.
When to use
- Use in adults aged 18 years and older when a current source requires the 2021 CKD-EPI equations.
- Use the creatinine-only result as the fast path; add standardized cystatin C when available and a combined estimate is useful.
- Add patient BSA only when an absolute/de-indexed eGFR in mL/min is needed for the workflow you are following.
Key limitations
- eGFR is an estimate, not measured GFR. Individual uncertainty remains even when the arithmetic is exact.
- Creatinine-based eGFR can be less reliable with unusual muscle mass, amputation, severe frailty, some diets or medicines, and during rapidly changing kidney function.
- Cystatin C has different non-GFR determinants. The combined equation is generally more accurate when both standardized markers are available, but it is not universally more accurate for every patient; measured GFR may be appropriate when estimation remains unreliable and accuracy is critical.
- For ages 18–25, NIDDK recommends referencing both the adult CKD-EPI estimate and the CKiD U25 estimate. This calculator provides the adult estimate only.
- CKD-EPI eGFR should not be used to assess kidney function during pregnancy; pregnancy renal guidance recommends serum creatinine assessment and pregnancy-specific clinical guidance.
- For transgender, nonbinary or intersex people, AACC/NKF guidance recommends calculating CKD-EPI 2021 eGFR with both male and female equation constants and interpreting the range in clinical context, especially around important thresholds.
- The indexed result in mL/min/1.73 m² is used for G categories. De-indexing by BSA produces an absolute mL/min estimate but does not convert eGFR into Cockcroft-Gault CrCl.
- Do not silently substitute CKD-EPI 2021 when a current medicine label, dosing reference or specialty protocol explicitly specifies another renal-function method.
What MedMaths does not decide
- Whether the patient has chronic kidney disease from one isolated result.
- Whether creatinine-only, combined creatinine-cystatin C, measured GFR or another renal estimate is best for a particular decision.
- Which renal-function estimate a specific medicine requires, or a medication dose or dose interval.
- Referral, dialysis, transplant or treatment decisions.
Evidence and method checks
- eGFR Equations for Adults — NIDDK / NIH
- New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race — New England Journal of Medicine / PubMed
- KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of CKD — KDIGO
- eGFR Calculators for Adults & Pediatrics — NIDDK / NIH
- AACC/NKF Guidance Document on Improving Equity in Chronic Kidney Disease Care — AACC / National Kidney Foundation
- Clinical practice guideline on pregnancy and renal disease — BMC Nephrology / PMC
- Determining Drug Dosing in Adults with Chronic Kidney Disease — NIDDK / NIH
- Race-agnostic eGFR for Medication-related Decisions in Adults — National Kidney Foundation
- National Kidney Foundation and U.S. Pharmacy Organizations Call for Transition to Race-Free eGFR in Medication Decision-Making — National Kidney Foundation, June 2026
Formula logic and known-value examples are checked as part of the MedMaths review process.
See how MedMaths checks calculator methods →Need to understand eGFR vs CrCl?
Use the calculator for the arithmetic. The eGFR vs CrCl guide explains indexed versus absolute units, why the numbers differ, medication-dosing history and how to follow a source that specifies one method.
Formula details, examples and FAQs
Review both 2021 CKD-EPI equations, two worked examples, G categories, common input mistakes and focused questions.
Formula details, examples and FAQs
Review both 2021 CKD-EPI equations, two worked examples, G categories, common input mistakes and focused questions.
CKD-EPI 2021 equations used here
Creatinine-only eGFRcr
In simple words
Uses standardized serum creatinine, age and sex-specific constants. MedMaths converts µmol/L to mg/dL before applying the equation.
Combined creatinine-cystatin C eGFRcr-cys
In simple words
Uses standardized serum creatinine and cystatin C together with age and sex-specific constants. It is a separate equation, not a correction added to the creatinine-only result.
Both equations were published by Inker and colleagues for the CKD-EPI Collaboration in 2021. The linked researcher profiles highlight first author Lesley A. Inker and senior author Andrew S. Levey without presenting them as the complete collaboration.
Worked eGFR examples
Example 1 — creatinine in µmol/L
- Male equation term, age 65 years
- Serum creatinine = 90 µmol/L
- 90 ÷ 88.4 = 1.018 mg/dL
- 2021 CKD-EPI eGFRcr = 81.7 mL/min/1.73 m²
Indexed category: G2
Example 2 — cystatin C and BSA
- Female equation term, age 58 years
- Creatinine = 1.10 mg/dL; cystatin C = 1.40 mg/L
- eGFRcr = 58.2 mL/min/1.73 m²
- eGFRcr-cys = 52.4 mL/min/1.73 m²
- With BSA 1.65 m², combined absolute eGFR = 50.0 mL/min
G category still uses the indexed result: G3a
CKD G-category reference
| Category | Indexed eGFR | Description |
|---|---|---|
| G1 | ≥90 | Normal or high |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mildly to moderately decreased |
| G3b | 30–44 | Moderately to severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | <15 | Kidney failure |
Values are mL/min/1.73 m². G category is only one part of CKD classification; albuminuria, cause and chronicity also matter.
Common eGFR calculator mistakes
Creatinine unit mismatch
Entering a µmol/L value while mg/dL is selected, or the reverse, can change the result dramatically.
Treating absolute eGFR as a G-category value
G categories use indexed mL/min/1.73 m², even when a BSA-adjusted mL/min result is also shown.
Assuming cystatin C is a simple correction
The combined 2021 equation is a separate formula with different coefficients.
Using one renal equation for every medicine
Follow the current medicine label, dosing reference, pharmacy guidance or clinical protocol.
Using steady-state equations during rapid change
A quickly rising or falling creatinine can make the calculated eGFR lag behind current filtration.
Diagnosing CKD from one number
One eGFR result does not establish chronicity, cause or the full CKD risk category.
Frequently Asked Questions
Continue calculating
Related renal and dosing calculators
Use these calculators when renal function connects to Cockcroft-Gault, body surface area or dosing-weight calculations.
Creatinine Clearance Calculator
Calculate adult Cockcroft-Gault CrCl when a medicine label, protocol or exam specifically requires this method.
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Calculate adult Devine ideal body weight in cm or feet and inches, with optional Robinson and Miller comparison estimates.
Open calculatorBSA Calculator
Calculate body surface area from metric or imperial height and weight using four published formulas.
Open calculatormg/kg to mL Dose Calculator
Calculate mg/kg per-dose or per-day orders using kg or lb, divided doses, and liquid concentration.
Open calculatorAnion Gap Calculator
Calculate anion gap from sodium, chloride and bicarbonate, with optional albumin correction.
Open calculatorReferences and sources
Open the primary equation paper plus current eGFR reporting, transition-age, gender-diversity, pregnancy and medication guidance used for this calculator.
References and sources
Open the primary equation paper plus current eGFR reporting, transition-age, gender-diversity, pregnancy and medication guidance used for this calculator.
Original 2021 CKD-EPI publication
Inker LA, Eneanya ND, Coresh J, et al. New Creatinine- and Cystatin C–Based Equations to Estimate GFR without Race. N Engl J Med. 2021;385(19):1737–1749.
PubMed PMID 34554658Adult equation definitions and accuracy
NIDDK. eGFR Equations for Adults — publishes the 2021 creatinine and creatinine-cystatin C equations, units and current accuracy notes.
NIDDK adult eGFR equationseGFR reporting and G-category standards
KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of CKD — recommends reporting adult eGFR to the nearest whole number, relative to 1.73 m², and provides current GFR-category context.
KDIGO 2024 CKD guidelineAges 18–25 transition guidance
NIDDK. eGFR Calculators for Adults & Pediatrics — recommends referencing both the adult CKD-EPI and CKiD U25 estimates for patients aged 18–25.
NIDDK adult and pediatric eGFR calculatorsGender-diverse eGFR interpretation
Pierre CC, et al. AACC/NKF Guidance Document on Improving Equity in Chronic Kidney Disease Care. J Appl Lab Med. 2023;8(4):789–816 — recommends calculating CKD-EPI 2021 eGFR with both male and female constants in transgender, nonbinary or intersex people.
AACC/NKF guidancePregnancy limitation
Wiles K, et al. Clinical practice guideline on pregnancy and renal disease. BMC Nephrol. 2019;20:401 — recommends serum creatinine assessment because eGFR is not valid for use in pregnancy.
Pregnancy and renal disease guidelineDrug dosing and BSA adjustment
NIDDK. Determining Drug Dosing in Adults with Chronic Kidney Disease — discusses contemporary eGFR equations, cystatin C near dosing thresholds and removal of BSA indexing when appropriate.
NIDDK drug-dosing guidance2026 medication-decision transition
National Kidney Foundation and U.S. pharmacy organisations. 2026 consensus implementation material supporting transition from Cockcroft-Gault toward race-free 2021 CKD-EPI eGFR for medication-related decisions in adults.
NKF medication-decision guidance