Corrected Calcium Calculator
Adjust total serum calcium for low albumin using the Payne formula.
This correction is intended for albumin below the normal range (roughly under 4 g/dL) — it has limited value when albumin is normal or high.
About 40% of blood calcium is bound to albumin, so a low albumin level makes total calcium look lower than the physiologically active (ionized) fraction really is. This correction adjusts for that, estimating what total calcium would read if albumin were normal.
An estimate, not the gold standard. A directly measured ionized calcium is more accurate than any corrected-calcium formula, especially in critically ill patients. Discuss abnormal results with a healthcare provider.
How corrected calcium is calculated
Payne formula (1973)
Published by Payne, Little, Williams, and Milner in the British Medical Journal in 1973, this remains the most widely taught correction formula for hypoalbuminemia in clinical training, despite newer studies questioning its precision compared with directly measured ionized calcium.
Common questions
About 40% of calcium in the blood is bound to albumin and isn’t biologically active; the rest is free (ionized) calcium, which is what matters physiologically. When albumin is low, total calcium reads lower than the ionized fraction alone would suggest — the correction estimates what total calcium would be if albumin were normal.