Your estimated levothyroxine starting dose is calculated based on your body weight and clinical indication. For full thyroid hormone replacement in primary hypothyroidism, the standard dose is approximately 1.6 mcg/kg/day, which provides adequate T4 to normalize TSH in most adults. For TSH suppression therapy (e.g., after thyroid cancer), higher doses near 2.0 mcg/kg/day are typically required to achieve a TSH below 0.1 mIU/L. For subclinical hypothyroidism or elderly patients, a conservative starting dose of approximately 1.0 mcg/kg/day or even 12.5–25 mcg/day is recommended to avoid cardiac complications.

This result is a starting point only. Levothyroxine dosing is highly individualized, and your actual requirement depends on residual thyroid function, body composition, absorption factors, and concomitant medications. TSH should be rechecked 6–8 weeks after initiation or any dose adjustment to guide titration.

Use this calculator when initiating levothyroxine therapy for a newly diagnosed hypothyroid patient, whether from autoimmune thyroiditis (Hashimoto's), post-thyroidectomy, post-radioactive iodine ablation, or subclinical hypothyroidism. It is also helpful when estimating a TSH suppression dose for differentiated thyroid cancer patients.

This tool is intended for adult dosing. Pediatric thyroid hormone dosing uses different weight-based calculations. It is most useful in the outpatient setting when starting therapy, though inpatient clinicians may also reference it when converting from IV levothyroxine (which is approximately 75% of the oral dose).

This calculator provides a weight-based estimate and does not account for factors that significantly alter levothyroxine requirements, including malabsorption syndromes (celiac disease, bariatric surgery), concurrent medications that reduce absorption (calcium, iron, PPIs, cholestyramine), pregnancy (which increases requirements by 25–50%), and age-related changes in metabolism.

The calculator assumes a standard oral bioavailability of approximately 70–80%. Actual doses are typically rounded to the nearest available tablet strength (25, 50, 75, 88, 100, 112, 125, 137, 150, 175, 200 mcg). Overreplacement carries risks of atrial fibrillation and osteoporosis, particularly in elderly patients, so conservative initiation with gradual titration is preferred in high-risk populations.