What dosing factor does this calculator use?

For primary hypothyroidism (full replacement), the standard factor is 1.6 mcg/kg/day of actual body weight, per the American Thyroid Association guidelines. For TSH suppression, mild suppression uses 2.0 mcg/kg/day and full suppression uses 2.4 mcg/kg/day.

Should ideal body weight be used instead of actual weight?

Most guidelines recommend actual body weight for levothyroxine dosing in non-obese patients. For obese patients (BMI > 30), some clinicians use adjusted or lean body weight. This calculator uses actual body weight; your physician may adjust accordingly.

Why is there a maximum dose cap?

Doses above 200–250 mcg/day are uncommon and may pose cardiovascular risks, especially in older patients. If the weight-based calculation exceeds this range, the tool shows a clinical note. The actual dose prescribed depends on individual patient factors.

How long does it take for levothyroxine to reach steady state?

Levothyroxine has a half-life of approximately 7 days. Steady state is typically reached after 6–8 weeks. TSH should be rechecked 6–8 weeks after initiating or changing dose.

Is this tool appropriate for elderly patients?

Elderly patients often require lower starting doses (0.25–0.5 mcg/kg/day) due to reduced clearance and cardiovascular sensitivity. This tool estimates standard adult doses — always apply clinical judgment for older or cardiac patients.

Can this replace a physician's prescription?

No. This tool provides an educational estimate only. Levothyroxine dosing requires individualized titration based on serial TSH levels, symptoms, age, cardiovascular status, and comorbidities. Always consult a licensed clinician before starting or adjusting therapy.

Levothyroxine Weight-Based Dose Calculator

Name: Levothyroxine Weight-Based Dose Calculator
Availability: InStock
Author: Nham Vu

Enter patient weight and indication to estimate an initial levothyroxine dose in mcg/day — always verify with a physician.

Patient Details

Patient Weight

Indication

For educational reference only. Levothyroxine dosing requires individualized titration based on serial TSH measurements and guidance from a licensed clinician. Do not adjust your dose based on this estimate alone.

Enter weight and indication to calculate the estimated starting dose.

Summary

Enter patient weight and indication to estimate an initial levothyroxine dose in mcg/day — always verify with a physician.

How it works

Enter patient weight in kilograms or pounds.
Select the clinical indication: hypothyroidism replacement or TSH suppression.
For TSH suppression, choose the suppression target (mild vs. full).
The calculator applies the standard mcg/kg/day dosing factor for the selected indication.
The estimated dose is displayed alongside the expected therapeutic range.
A note appears if the calculated dose exceeds the typical clinical maximum.

Use cases

Estimate a starting levothyroxine dose for a newly diagnosed hypothyroid patient.
Calculate TSH-suppressive dose for differentiated thyroid cancer post-thyroidectomy.
Check whether a current prescription is within the standard weight-based range.
Educate patients on how their dose relates to their body weight.
Support clinical pharmacology and endocrinology coursework.
Compare full-replacement vs. suppressive dosing for the same patient weight.
Identify doses that may warrant dose-capping due to cardiovascular risk.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu