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Levothyroxine Dosage for Hypothyroidism

Calculate thyroid hormone replacement dosing. Base: 1.6 mcg/kg/day. Adjust for elderly, cardiac, pregnancy, and subclinical hypothyroidism.

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Base: 1.6 mcg/kg/day Elderly: start 25-50 mcg Cardiac: start 12.5-25 mcg Pregnancy: +30-50%

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Why: Proper levothyroxine dosing normalizes TSH and relieves hypothyroid symptoms while avoiding over-replacement.

How: Weight-based calculation with adjustments for age, cardiac, pregnancy, and absorption factors.

Base: 1.6 mcg/kg/dayElderly: start 25-50 mcg
Sources:ATA Guidelines

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Calculate Your DoseUse the calculator below to check your health metrics

🩺 New Diagnosis - Young Adult

35-year-old female with newly diagnosed primary hypothyroidism, TSH 45 mIU/L

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❤️ Elderly with Cardiac History

72-year-old male with hypothyroidism and coronary artery disease, requiring cautious dosing

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🤰 Pregnant Patient

28-year-old female in first trimester with known hypothyroidism requiring dose adjustment

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🏥 Post-Thyroidectomy

50-year-old female after total thyroidectomy for thyroid cancer, requiring full replacement

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📊 Subclinical Hypothyroidism

45-year-old female with subclinical hypothyroidism, TSH 8.5 with normal free T4

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Patient Information

Patient Demographics

Patient body weight for dose calculation
Affects starting dose and target TSH
Sex for reference values

Clinical Parameters

Type affects dosing strategy
Most recent TSH value
Free T4 level (normal: 0.8-1.8)

Risk Factors

Cardiac disease requires cautious dosing
Pregnancy increases thyroid hormone needs
Factors affecting absorption

Current Therapy

Current levothyroxine dose if applicable

For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.

🏥 Health Facts

⚠️

Take on empty stomach 30-60 min before breakfast. Separate from calcium/iron by 4 hours.

— ATA

What is Levothyroxine?

Levothyroxine is a synthetic form of thyroxine (T4), the main hormone produced by the thyroid gland. It is the standard treatment for hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone.

Standard Dosing

Full replacement dose is 1.6 mcg/kg/day for most adults with primary hypothyroidism and no cardiac disease.

TSH Target

Goal TSH is typically 0.5-2.5 mIU/L for most patients, with higher targets acceptable in elderly.

Monitoring

Check TSH 6 weeks after any dose change, then every 6-12 months when stable.

How Levothyroxine Dosing Works

Weight-Based Calculation

  1. 1. Calculate base dose: Weight × 1.6 mcg/kg
  2. 2. Apply age adjustment (elderly: 0.7×)
  3. 3. Apply cardiac adjustment (0.5×)
  4. 4. Apply pregnancy adjustment (1.3-1.4×)
  5. 5. Round to nearest available tablet

Special Populations

  • • Elderly: Start 25-50 mcg, titrate slowly
  • • Cardiac: Start 12.5-25 mcg
  • • Pregnancy: Increase dose 30-50%
  • • Subclinical: Start 25-50 mcg

Levothyroxine Dosing Formula

Full Replacement Dose

Dose (mcg/day) = Weight (kg) × 1.6 mcg/kg

Dose Adjustment

Adjusted Dose = Base Dose × Adjustment Factor

Factors: Elderly (0.7), Cardiac (0.5), Pregnancy (1.3-1.4)

When to Adjust Levothyroxine Dose

Increase Dose When:

  • • Pregnancy confirmed
  • • Weight gain significant
  • • Malabsorption suspected
  • • New drug interactions
  • • TSH persistently elevated

Decrease Dose When:

  • • TSH suppressed (<0.4)
  • • Hyperthyroid symptoms
  • • Significant weight loss
  • • Elderly (age adjustment)
  • • Cardiac symptoms emerge

Keep Stable When:

  • • TSH in target range
  • • Patient feels well
  • • No medication changes
  • • Weight stable
  • • No new symptoms

Important Drug Interactions

Decreased Absorption

Take levothyroxine 4 hours apart from these medications:

  • • Calcium supplements
  • • Iron supplements
  • • Antacids (aluminum/magnesium)
  • • Proton pump inhibitors
  • • Cholestyramine, sucralfate
  • • Soy products, coffee

Increased Metabolism

These drugs may increase levothyroxine requirements:

  • • Phenytoin, carbamazepine
  • • Phenobarbital
  • • Rifampin
  • • Estrogen therapy
  • • Sertraline

Administration Best Practices

Optimal Timing

  • Take on empty stomach, ideally 30-60 min before breakfast
  • Alternative: bedtime, at least 3 hours after eating
  • Take with water only

Consistency Tips

  • Take at the same time daily
  • Don't switch brands without rechecking TSH
  • If dose missed, take when remembered (unless near next dose)
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