What dose does this calculator use?

For full replacement in otherwise healthy adults, the calculator uses a weight-based range around the widely cited 1.6 mcg/kg/day dose. For elderly patients or those with underlying cardiac disease, it shows the labeled conservative starting range of 12.5–25 mcg/day rather than scaling the initial dose by weight. These are educational starting-point estimates only.

Can I use this to self-prescribe levothyroxine?

No. Levothyroxine is a prescription medication in most countries. This tool is strictly educational. Your actual dose must be determined and monitored by a licensed physician using TSH blood tests.

Why are doses rounded to the nearest 25 mcg?

For weight-based modes, the midpoint is rounded to 25 mcg as a simple practical illustration. The elderly and cardiac modes retain the labeled 12.5–25 mcg/day starting range instead. Actual tablet selection, splitting, and titration must be prescribed by a clinician.

What is TSH and why does it matter?

TSH (thyroid-stimulating hormone) is the primary lab marker used to monitor levothyroxine therapy. A normal TSH range is typically 0.4–4.0 mIU/L. Dose adjustments are made based on TSH results every 6–8 weeks until stable.

Does weight alone determine the correct dose?

No. Weight is a starting-point predictor only. Residual thyroid function, age, cardiovascular status, pregnancy, and drug interactions all influence the final dose. Only serial TSH monitoring confirms adequacy.

How often should the dose be reviewed?

TSH should be checked 6–8 weeks after starting or changing the dose. Once stable, annual monitoring is typical for most patients, with more frequent checks during pregnancy or after significant weight change.

Levothyroxine Dose Calculator

Estimate a weight-based starting levothyroxine dose for hypothyroidism — for educational reference only, not medical advice.

Patient Details

For educational reference only — not a substitute for medical advice.

Body Weight

Clinical Condition

Enter patient details and click
Calculate Dose

Summary

Estimate a weight-based starting levothyroxine dose for hypothyroidism — for educational reference only, not medical advice.

How it works

Enter your body weight and select kilograms or pounds.
Choose your clinical condition from the dropdown (e.g., primary hypothyroidism, elderly patient, cardiac disease).
Click "Calculate Dose" to see the estimated starting dose range.
Review the educational notes about titration and monitoring.
Share the result with your physician — never self-prescribe based on this estimate.

Use cases

Quickly cross-check a physician-prescribed starting dose against published weight-based guidelines.
Educate patients about why dose varies by weight and health status.
Help pharmacy students and nurses understand dosing principles for hypothyroidism.
Support clinical educators teaching thyroid hormone replacement concepts.
Estimate dose adjustments when body weight changes significantly.
Compare full-replacement vs. conservative dosing for different patient profiles.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu