MDCalc presents this as a full oral replacement-dose estimate from body weight for adult hypothyroidism.

American Thyroid Association hypothyroidism guidelines support levothyroxine as standard therapy and describe weight-based full replacement dosing for patients with minimal endogenous thyroid function, while noting that actual weight, ideal weight, age, pregnancy, a TSH-suppression target and comorbidity can change requirements.

Levothyroxine labeling lists 1.6 mcg/kg/day as a full replacement dose for adults diagnosed with hypothyroidism, with lower starts for geriatric patients and adults with atrial-fibrillation risk or underlying cardiac disease.

Older adults and cardiac disease: lower starting doses and slower titration are usually preferred to reduce the risk of precipitating cardiac symptoms.
Pregnancy: levothyroxine requirements and TSH targets differ. Use pregnancy-specific guidance.
Obesity: actual body weight may overestimate requirements. Ideal body weight or lean body mass may better reflect dose need.
Monitoring: adjust therapy to TSH and clinical response, commonly reassessing 4-8 weeks after initiation or dose changes.

Weight-Based Levothyroxine Starting Dose (Adults)