GFR Calculator

What glomerular filtration rate measures

GFR is the volume of plasma the glomeruli filter per minute.

Labs report an estimate indexed to 1.73 m² of body surface area (mL/min/1.73 m²) so people of different size can be compared. The number comes from creatinine, age, and sex. It is not a picture of one nephron.

True GFR uses exogenous markers such as iohexol or iothalamate. Those tests belong in transplant work, research, and cases where creatinine is a poor stand-in for muscle mass. For ordinary adult care, NKF and NIDDK recommend the 2021 CKD-EPI creatinine equation. Creatinine is made in muscle and leaves by filtration plus some tubular secretion, so a muscular adult can have a higher creatinine at the same GFR as someone with little muscle. The equation uses average age and sex effects. It cannot see amputation, paralysis, anabolic steroids, or a very low-meat diet.

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The 2021 CKD-EPI creatinine equation

eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^-1.200 × 0.9938^age × 1.012 if female. Inker and colleagues published that single-expression 2021 CKD-EPI creatinine equation. NKF and NIDDK reproduce it. Scr is mg/dL. κ is 0.7 in females and 0.9 in males. α is -0.241 in females and -0.302 in males.

Select µmol/L and the page divides by 88.4. Age is whole years, 18 and up. Pediatric reporting uses other equations.

The 2021 fit dropped the race term. NKF and ASN asked labs to replace MDRD and the 2009 CKD-EPI creatinine equation (Black/non-Black coefficient) with this version. Do not plot 2009 or MDRD values on the same trend as 2021 results.

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Worked eGFR examples

A 60-year-old woman with creatinine 1.0 mg/dL: Scr/κ = 1.43, min = 1, max = 1.43. 142 × 1.43^-1.200 × 0.9938^60 × 1.012 rounds to 65 mL/min/1.73 m² (G2).

A 70-year-old man with creatinine 1.2 lands near the same 65. Age, sex, and creatinine differ. A raw creatinine of 1.2 is not a kidney-function result by itself. A 45-year-old woman at 0.6 sits below the 0.7 knot, so α applies to Scr/κ instead of the -1.200 limb. The estimate is about 113 (G1).

Display rounding to a whole number is fine. A 1 mL/min/1.73 m² wobble is not a new stage.

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How to use the GFR calculator

Enter adult age, sex as the lab equation uses it, and an IDMS serum creatinine in the unit on the report.

G1 is 90 or higher, G2 is 60 to 89, G3a 45 to 59, G3b 30 to 44, G4 15 to 29, G5 below 15. Read eGFR and the G letter together. G1 or G2 without kidney damage (for example albuminuria) is not CKD.

A clinician should recompute with the current lab method, and often cystatin C, before the number changes a drug, transplant listing, or contrast plan. This page does not convert indexed eGFR to mL/min for body size. Dosing in mL/min needs that step. Keep strips and lab creatinines off the same trend line.

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KDIGO GFR categories and CKD

KDIGO stages CKD by cause, GFR category, and albuminuria (CGA).

G1 through G5 use the table below. Albuminuria is A1, A2, or A3 from a urine ACR. Persistent A3 with a G1 eGFR is still CKD. CKD means structure or function problems lasting more than 3 months. An eGFR of 58 during gastroenteritis is not a G3a diagnosis. Repeat creatinine when volume is restored and add an ACR.

NIDDK wants ACR in people at kidney risk. eGFR plus ACR predicts kidney failure and cardiovascular events better than either marker alone.

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How to read the creatinine on the report

Use a venous IDMS lab creatinine when the number will guide care. Most U.S. labs have used standardized creatinine for more than a decade. A 1990s non-standardized value does not belong in 2021 CKD-EPI. Skip dried-blood consumer kits for that job.

No need to fast.

A large cooked-meat meal the day before can lift creatinine and blur a G2/G3a border. Extreme exercise, creatine supplements, trimethoprim, cimetidine, and some secretion-blocking antibiotics raise creatinine without a matching GFR drop. Pregnancy, amputation, neuromuscular disease, and high-dose glucocorticoids change the creatinine-GFR relationship. Ask for cystatin C or a measured GFR there instead of hitting calculate again.

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What to do with the result

eGFR 60 or higher without albuminuria, hypertension, diabetes, or hematuria is a baseline. Recheck on the usual preventive schedule.

At 45 to 59, confirm on a second sample, measure ACR, review ACE inhibitors, ARBs, SGLT2 inhibitors, NSAIDs, and diuretics, and look at blood pressure and glucose. Persistent G3b or worse, a fast fall, A3 albuminuria, or unexplained hematuria usually goes to nephrology. Referral cutoffs still vary by clinic.

A lower eGFR than last year is not a reason to stop a prescribed drug. Metformin, DOACs, gabapentin, and many antimicrobials need the label, current weight, and a clinician. Indexed eGFR (mL/min/1.73 m²) is not unindexed clearance (mL/min). Multiply indexed eGFR by BSA/1.73: BSA 2.1 m² and indexed 50 is about 61 mL/min; BSA 1.4 m² and the same 50 is about 40. Transplant and some drug decisions want that unindexed number.

Older reports printed “>60” because MDRD was poor at high filtration. 2021 CKD-EPI prints a number. “>60” last year and 64 now is often a reporting change.

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Accuracy limits and safety

Group performance is acceptable. People are still misclassified.

NIDDK cites about 4% overestimation in non-Black adults and 4% underestimation in Black adults versus measured GFR. That average is not your error bar. Skip this equation in AKI, dialysis, anuria, and extreme age or body size. Under 18, the page returns a message. Use CKiD or bedside Schwartz.

Obstruction, glomerulonephritis, and polycystic disease need imaging, sediment, and a cause workup. No urine, pulmonary edema, or hyperkalemia is urgent care, not another eGFR.

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How it works

eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^-1.200 × 0.9938^age × 1.012 if female. κ is 0.7 in females and 0.9 in males. α is -0.241 in females and -0.302 in males. Creatinine is in mg/dL.

Frequently asked questions

• Is this the same as a lab eGFR?Many U.S. labs now report the 2021 CKD-EPI creatinine equation. Confirm the equation name on the report. Older MDRD or 2009 CKD-EPI values should not be trended against this result.
• Does a G3a result mean I have CKD?CKD requires reduced GFR or kidney damage lasting at least three months. A single eGFR below 60 is a prompt for repeat testing and albuminuria assessment, not a diagnosis by itself.
• Why is there no race field?The 2021 CKD-EPI creatinine equation was refit without a race coefficient. NKF and ASN recommend this race-free equation for adult reporting.

Related calculators

References

1. NIDDK. Estimated Glomerular Filtration Rate Calculators
2. National Kidney Foundation. CKD-EPI Creatinine Equation (2021)
3. Inker et al., 2021. New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race
4. NIDDK. eGFR Equations for Adults
5. KDIGO. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease
6. KDIGO 2024. CKD classification by GFR and albuminuria (CGA)
7. Miller et al.. Laboratory implementation of CKD-EPI 2021
8. NIDDK. About Chronic Kidney Disease