Levothyroxine Starting Dose
This calculator provides an estimated starting dose of levothyroxine (LT4) based on body weight and clinical indication. Final dose is always individualized and titrated to TSH response.
Estimated Starting Dose
—
mcg/day (once daily, morning fasting)
Nearest available tablet strengths:
Dosing basis: 1.6 mcg/kg/day for full replacement · 1.6–1.8 mcg/kg/day post-thyroidectomy · TSH suppression (high-risk DTC): target TSH 0.1–0.5 mU/L (≈1.8–2.2 mcg/kg/day) · Elderly/cardiac: start 25–50 mcg regardless of weight, titrate slowly.
Available LT4 strengths (mcg): 25, 50, 75, 88, 100, 112, 125, 137, 150, 175, 200, 300
Available LT4 strengths (mcg): 25, 50, 75, 88, 100, 112, 125, 137, 150, 175, 200, 300
Levothyroxine Dosing Reference
| Indication | Starting Dose | TSH Target | Follow-up |
|---|---|---|---|
| Primary hypothyroidism (full replacement) | 1.6 mcg/kg/day | 0.4–4.0 mU/L | 6–8 weeks |
| Post-total thyroidectomy (low-risk DTC) | 1.6 mcg/kg/day | 0.5–2.0 mU/L | 6–8 weeks |
| Post-thyroidectomy (high-risk DTC) | 1.8–2.2 mcg/kg/day | 0.1–0.5 mU/L | 6–8 weeks |
| Subclinical hypothyroidism | 25–50 mcg/day | 0.4–4.0 mU/L | 6–8 weeks |
| Central hypothyroidism | 1.6 mcg/kg/day | Free T4 mid-normal | 6–8 weeks |
| Age ≥ 65 or cardiac disease | 12.5–25 mcg/day start | 0.4–4.0 mU/L | 6–8 weeks |
| Pregnancy | Increase dose by ~30% | 0.1–2.5 mU/L (1st tri) | Every 4 weeks |
Key interactions affecting LT4 absorption: Take 30–60 min before food/coffee. Separate from calcium, iron, antacids (4h), and cholestyramine. Proton pump inhibitors and bariatric surgery may require dose increase. Pregnancy increases requirement by 25–50%.
⚕️ Clinical note: This is an estimated starting dose only. Actual dose must be individualized and titrated based on TSH (and free T4 for central hypothyroidism) measured 6–8 weeks after initiation or dose change. Patients with cardiac disease, adrenal insufficiency, or severe hypothyroidism (myxedema) require special management. Levothyroxine has a narrow therapeutic index — use consistent formulations. Doses shown are for oral levothyroxine sodium (e.g., Synthroid, Levoxyl, generic). Always confirm with your prescribing provider. Based on ATA 2014 guidelines (Jonklaas J et al., Thyroid 2014).