Levothyroxine Weight-Based Dosing
Calculate suggested starting or maintenance doses for levothyroxine using guideline-based mcg/kg targets. Always confirm with thyroid function tests.
Full replacement ~1.6 mcg/kg/day.
Enter 0 if patient is levothyroxine-naïve.
Dose Suggestion
Calculated dose
112 mcg/day
Weight: 70.0 kg • 1.6 mcg/kg.
Rounded tablet strength
112 mcg/day
Starting dose. Recheck TSH in 6–8 weeks.
How to Use This Calculator
Select the clinical scenario
Different populations need different mcg/kg targets to avoid over-treatment.
Enter weight and current dose
The calculator suggests a target and compares it with current therapy.
Round to available strengths
Levothyroxine tablets come in specific strengths—round to the nearest feasible option.
Formula
Daily dose (mcg) = weight (kg) × mcg/kg (1.6 mcg/kg healthy adults).
Derived from ATA/AACE hypothyroidism guidelines and Endocrine Society recommendations.
Frequently Asked Questions
How often should TSH be monitored?
Check TSH 6–8 weeks after dose changes, then every 6–12 months once stable.
Should I use actual or ideal body weight?
Use actual weight unless BMI >30; in obesity consider lean body weight (IBW + 0.2 × (actual − IBW)).
What about pregnancy?
Increase dose by ~30% at confirmation (take 2 extra tablets weekly) and monitor TSH monthly.
Can doses vary during the week?
Yes. Average weekly dose matters; use pill boxes or alternate daily doses as needed.
What medications interfere with absorption?
Calcium, iron, PPIs, sucralfate, soy. Separate by at least 4 hours.