Wells Score Calculator
The Only Criterion That Subtracts
Most clinical scoring systems only ever add. The Wells criteria for deep vein thrombosis are unusual in containing a negative item: if an alternative diagnosis is at least as likely as DVT, the score drops by two points. That single subtraction is what makes Wells a genuine pre-test probability tool rather than a checklist — it forces the assessor to weigh what else could explain the leg, not merely to tally what supports one answer.
The Criteria
This calculator applies the nine criteria exactly as scored:
| Criterion | Points |
|---|---|
| Active cancer (treatment ongoing, within 6 months, or palliative) | +1 |
| Paralysis, paresis, or recent plaster immobilization of the lower extremities | +1 |
| Recently bedridden more than 3 days, or major surgery within 12 weeks | +1 |
| Localized tenderness along the deep venous system | +1 |
| Entire leg swollen | +1 |
| Calf swelling more than 3 cm compared to the asymptomatic leg | +1 |
| Pitting edema confined to the symptomatic leg | +1 |
| Collateral superficial veins (non-varicose) | +1 |
| Alternative diagnosis at least as likely as DVT | −2 |
The Formula
Score < 1 → Low probability of DVT
Score 1–2 → Moderate probability of DVT
Score ≥ 3 → High probability of DVT
Because of the −2 item, the score has a floor of −2 and a ceiling of +8. A patient with two positive findings and a compelling alternative explanation lands at zero — the low band — which is precisely the discrimination the negative item was designed to produce.
The Cluster Problem
Several of the positive criteria describe overlapping physical findings: whole-leg swelling, calf swelling over 3 cm, and pitting edema will frequently travel together in the same leg. This is not an oversight. The criteria were derived empirically from what predicted DVT in validation cohorts, not designed for statistical independence. It does mean the score can climb quickly once a leg is genuinely swollen, which is part of why the high band is a trigger for imaging rather than a conclusion.
Where This Score Fits
- Structuring a diagnostic pathway — Wells is a pre-test probability estimate that determines what happens next, typically D-dimer testing or ultrasound, rather than answering the question itself.
- Reducing unnecessary imaging — the low-probability band, combined with a negative D-dimer, is the classic combination used to avoid scanning legs that do not need it.
- Documentation — recording a Wells score makes clinical reasoning explicit and auditable.
- Teaching — it is a standard worked example of how pre-test probability shapes the value of a subsequent test.
Score Distribution and Bands
The three probability bands across the full range the Wells score can occupy.
How to Use This Calculator
- Work down the nine checkboxes, ticking each criterion that is present.
- Give particular thought to the final item — whether an alternative diagnosis is at least as likely — since it is the only one that subtracts, and it moves the total by two.
- Select Calculate. The output lists every criterion with its contribution marked present or absent, then reports the total and the probability band.
Related Calculations
For another point-based clinical scoring scheme, see the CHA²DS²-VASc Calculator, or examine risk-factor tallying in a cardiovascular context with the Heart Attack Risk Calculator.