Corrected calcium = measured calcium + 0.8 × (4 − albumin), with calcium in mg/dL and albumin in g/dL.
The correction is an approximation and it is unreliable in critical illness and in advanced kidney disease. Where the answer changes what you would do, measure ionised calcium instead.
It is a calculator, not a clinician. Nothing here is medical advice, and the person prescribing owns the decision.