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Levothyroxine Starting Dose (Weight-Based)

Full replacement levothyroxine is about 1.6 mcg/kg/day (actual, or ideal body weight in obesity). Older patients (≈ >60–65) without coronary disease usually start at 50 mcg/day, and those with known or suspected coronary artery disease at 12.5–25 mcg/day, titrating every 6–8 weeks to TSH (ATA 2014).

  • Weight (kg or lb)
  • Patient group: Younger healthy adult with overt hypothyroidism; Older adult (≈ > 60–65) without coronary disease; Known or suspected coronary artery disease
  • Weight used: Actual body weight; Ideal body weight (obesity)
  • Height (cm or m or in)
  • Sex: Male; Female
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Interpretation

ResultMeaning
Healthy younger adult1.6 mcg/kg/day full replacement
Older, no CADStart 50 mcg/day
Coronary diseaseStart 12.5–25 mcg/day
AllRecheck TSH 6–8 weeks after each change

Formula

Full replacement dose (mcg/day) = 1.6 × weight (kg). Ideal body weight (Devine): 50 kg (men) or 45.5 kg (women) + 2.3 kg per inch over 60 in.

Clinical pearls

  • Subclinical hypothyroidism usually needs much less (often 25–75 mcg/day); full weight-based dosing applies to overt hypothyroidism or post-thyroidectomy.
  • In obesity, actual-weight dosing tends to overshoot because requirement tracks lean mass; consider ideal body weight.
  • Take on an empty stomach, 30–60 minutes before breakfast and apart from calcium, iron and PPIs. Pregnancy typically needs a 20–30% dose increase.

Examples

levothyroxine dose 70 kgsynthroid starting dose for 78 yo with CAD 80 kglevothyroxine for obese woman 110 kg 163 cm using ideal body weight

FAQ

How is the levothyroxine dose calculated?

Full replacement is about 1.6 mcg per kg per day; a 70 kg adult needs roughly 112 mcg/day.

What starting dose should elderly patients get?

Older adults without coronary disease usually start at 50 mcg/day and patients with coronary disease at 12.5–25 mcg/day, increasing slowly.

Evidence

  1. Jonklaas J et al. Guidelines for the treatment of hypothyroidism: prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement. Thyroid 2014;24:1670–751.

Endocrine & Metabolic · Reviewed 2026-10-14 · Methodology