Corrected Calcium Calculator
Total calcium changes with albumin. This adjusts your measured calcium to what it would be at a normal albumin of 4.0 g/dL.
| Result | Interpretation |
|---|---|
| Below 8.5 | Low (hypocalcemia) |
| 8.5 to 10.3 | Normal |
| 10.3 and above | High (hypercalcemia) |
Source: Payne RB, Little AJ, Williams RB, Milner JR. Interpretation of serum calcium in patients with abnormal serum proteins. Br Med J 1973;4(5893):643-646. (doi:10.1136/bmj.4.5893.643)
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Corrected calcium formula
Corrected calcium (mg/dL) = measured calcium + 0.8 × (4.0 − albumin in g/dL)
This is the Payne formula. It adds 0.8 mg/dL of calcium for every 1 g/dL that albumin falls below 4.0, and subtracts the same amount when albumin is above 4.0.
If your lab reports in SI units, the same formula reads:
Corrected calcium (mmol/L) = measured calcium + 0.02 × (40 − albumin in g/L)
Worked example
Measured calcium 8.0 mg/dL with an albumin of 2.5 g/dL:
- 4.0 − 2.5 = 1.5
- 0.8 × 1.5 = 1.2
- 8.0 + 1.2 = 9.2 mg/dL, which is normal
A calcium that looked low on the lab report is normal once the low albumin is accounted for.
Quick correction chart
How much to add to the measured calcium for a given albumin:
| Albumin (g/dL) | Add to measured calcium (mg/dL) |
|---|---|
| 4.0 | 0 |
| 3.5 | 0.4 |
| 3.0 | 0.8 |
| 2.5 | 1.2 |
| 2.0 | 1.6 |
| 1.5 | 2.0 |
A normal corrected calcium is roughly 8.5 to 10.2 mg/dL (about 2.12 to 2.55 mmol/L).
When not to rely on it
The correction is an estimate. It is least reliable in exactly the patients where calcium matters most: critical illness, advanced kidney disease, and very low albumin. In those situations, ask for an ionized calcium, which measures the free calcium directly. There is no formula that turns a total calcium into an ionized calcium reliably.
FAQs
Why correct calcium for albumin?
About half of the calcium in your blood is bound to albumin. When albumin is low, the measured total calcium can look low even when the active, free calcium is normal. Correcting for albumin gives a value that better reflects true calcium status.
What formula is used?
Corrected calcium in mg/dL equals the measured calcium plus 0.8 times the quantity 4.0 minus your albumin in g/dL. In SI units, add 0.02 mmol/L for every g/L that albumin falls below 40.
Can I calculate ionized calcium from total calcium?
Not reliably. Ionized calcium has to be measured. If the corrected value and your symptoms do not fit together, ask your physician about an ionized calcium test.
What is a normal corrected calcium?
Roughly 8.5 to 10.2 mg/dL is considered normal. Values below or above that range should be interpreted by your physician, ideally with an ionized calcium where needed.