Switch to g/L if your lab reports SI. 40 g/L is 4.0 g/dL.
The equation, and where it comes from
Corrected calcium = measured calcium + 0.8 x (4.0 - albumin in g/dL)
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.
How to read the result
Typical adult reference range for total calcium is about 8.5 to 10.2 mg/dL. Where an ionised calcium is available it is the more reliable measurement, and this correction is an approximation rather than a substitute for it.
Your patient's numbers never leave this device
The corrected calcium arithmetic runs in JavaScript inside your own browser. There is no server call when you type, nothing is written to a database, nothing is logged, and no account is involved. Once the page has loaded you can disconnect from the network and it still works.
That matters more here than on an ordinary calculator. Values entered on a hospital workstation come off a real chart, and this tool deliberately does not remember them: close the tab and they are gone, including for the next person who uses that machine.
Frequently asked questions
- What is the corrected calcium formula?
- Corrected calcium = measured total calcium + 0.8 x (4.0 - albumin in g/dL). In SI units the equivalent is calcium in mmol/L + 0.02 x (40 - albumin in g/L). The constant comes from Payne's 1973 paper in the British Medical Journal.
- Why does albumin change the calcium reading?
- Around 40 percent of calcium in serum is bound to albumin and is not physiologically active. A total calcium assay measures bound and free together, so a patient with a low albumin can show a low total calcium while their ionised calcium, the fraction that actually matters, is perfectly normal.
- Is corrected calcium as good as an ionised calcium?
- No, and it is worth being clear about that. The correction is a population-average approximation, and it performs poorly in critical illness, in renal failure and in acid-base disturbance, because pH itself shifts calcium binding. Where a direct ionised calcium is available, measure it.
- When is the correction not worth doing?
- When albumin is already within its normal range, the adjustment moves the number by a trivial amount and adds nothing. This calculator says so explicitly when you enter an albumin between 3.5 and 5.0 g/dL, rather than presenting a false sense of precision.
- Can I enter mmol/L and g/L?
- Yes, both fields carry a unit switcher and the conversion runs before the equation. Calcium in mmol/L is multiplied by 4.008 to reach mg/dL, and albumin in g/L is divided by 10 to reach g/dL. The corrected result is reported in mg/dL whichever units you entered, so divide it by 4.008 if you need it back in mmol/L.