Winter's Formula Calculator

Winter's Formula Calculator for Nephrology. This implementation returns a code, not the expected pressure: 0 means within range, 1 below range and 2 above range. A within-range PCO2 does not exclude simultaneous metabolic disorders.

For shared guidance on choosing a tool and documenting results, read the clinical calculator workflow.

How this calculator works

For an established primary metabolic acidosis, expected arterial PCO2 is approximately 1.5 x bicarbonate + 8 mmHg, conventionally compared with a range 2 mmHg either side.

When to use this calculator

To compare an arterial blood-gas PCO2 with expected respiratory compensation after identifying the primary acid-base disorder.

Inputs used

  • Bicarbonate in mEq/L
  • Measured arterial PCO2 in mmHg (required for category output)

Clinical interpretation

This implementation returns a code, not the expected pressure: 0 means within range, 1 below range and 2 above range. A within-range PCO2 does not exclude simultaneous metabolic disorders.

Worked example

Bicarbonate 10 mEq/L gives expected PCO2 of 23 mmHg and comparison range 21-25. A measured 26 is above that range and prompts assessment for an additional respiratory process; it is not proof from arithmetic alone.

Limitations and safety notes

The relationship is approximate. Sample type, timing, ventilation and the underlying disorder matter. Do not use it for primary respiratory disorders or assume that any low bicarbonate establishes metabolic acidosis.

Frequently asked questions

Is a displayed 2 an expected PCO2 of 2 mmHg?

No. It is the component's category code for measured PCO2 above the comparison range.

Does compensated mean pH must be normal?

No. Expected respiratory compensation and normal pH are different concepts.

References

  • Marano M et al. Evaluation of Expected Ventilatory Response to Metabolic Acidosis in Severely Ill Patients. 2021. PMID: 34781612. https://pubmed.ncbi.nlm.nih.gov/34781612/
  • Albert MS, Dell RB, Winters RW. Quantitative displacement of acid-base equilibrium in metabolic acidosis. 1967. PMID: 6016545. https://pubmed.ncbi.nlm.nih.gov/6016545/
  • ASN Kidney Week 2020. Compensatory formulas for simple acid-base disorders. https://www.asn-online.org/education/kidneyweek/2020/program-abstract.aspx?controlId=3438332

Editorial review and citation methodology

Maintained by the Quick Medical Calculator Editorial Team. Content record date: September 7, 2026. A content date is not evidence of independent clinical review. Individual clinical sign-off is not recorded on this page.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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