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 calculator be used for pediatric dosing?

No. This calculator is strictly for adult patients (≥ 35 kg). Pediatric and congenital hypothyroidism require significantly higher, age-stratified starting doses (often 8–15 mcg/kg/day in infants) that must be managed by a pediatric specialist.

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

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

Adult Patient Details

Adult Patient Weight

Indication

For adult educational reference only. Pediatric and congenital hypothyroidism require specialized age-stratified regimens. 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

This calculator estimates a starting adult levothyroxine (T4) dose based on actual body weight using standard clinical dosing factors. Two indications are supported: full replacement for primary hypothyroidism (1.6 mcg/kg/day) and TSH-suppressive dosing for thyroid cancer or nodule management (2.0–2.4 mcg/kg/day). Results include the estimated dose, the applicable dosing range, and a capped maximum based on common clinical practice. This tool is for adult educational reference only — pediatric dosing requires specialized age-based regimens, and individual titration must be guided by serial TSH measurements and a qualified clinician.

How it works

Enter adult patient weight in kilograms or pounds (minimum 35 kg / 77 lb).
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: 2026-06-14 · Reviewed by Nham Vu

Levothyroxine Weight-Based Dose Calculator

Adult Patient Details

Typical Dose Range for This Indication

Clinical Notes

Summary

How it works

Use cases

Frequently Asked Questions

Levothyroxine Weight-Based Dose Calculator

Use the Levothyroxine Weight-Based Dose Calculator

Adult Patient Details

Typical Dose Range for This Indication

Clinical Notes

Summary

How it works

Use cases

Frequently Asked Questions