Levothyroxine Dosage Calculator

Written by Great Medico

Updated September 24, 2026 •2 min read

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A dose number is useful only when its assumptions are clear. Levothyroxine Dosage Calculator turns the selected medication details into the specific reference calculation implemented here, while keeping clinical prescribing separate from arithmetic.

What this calculator does

Levothyroxine Dosage Calculator uses Sex, Age, Weight, Height, Current level of FT4, and Heart disease to produce the reference starting-dose estimate used by this calculator. It only uses the fields shown in this calculator; it does not silently add tests, diagnoses, symptoms, or clinical variables that are absent from the interface. Mirrors the personal-information and health-condition flow. Uses actual or Devine ideal body weight as appropriate; dose output is an educational starting-dose estimate.

How to use it

Enter or select Sex, Age, Weight, Height, Current level of FT4, and Heart disease. Double-check the medication, route or formulation choices, weight/unit conversions, and concentration before relying on the output. If an input is unknown, it is better to leave the calculation unresolved than to invent a value.

How the calculation works

The engine estimates Devine ideal body weight from sex and height, then uses the lower of actual weight and that ideal-body-weight estimate. For the low-FT4 branch it uses 1.6 micrograms/kg/day unless age or heart-disease rules supersede it; heart disease returns 25 micrograms/day, age 65 or older returns 50 micrograms/day, and the normal-FT4 branch is constrained to a 25–75 microgram/day reference range.

Example

Using the calculator’s prefilled demonstration values, the primary output is 91.1 µg/day, labeled “Reference starting-dose estimate”; Weight used is 56.9 kg and Devine IBW is 56.9 kg. That sample is useful for checking the calculation path, but real interpretation should use verified measurements from the same clinical or study context.

How to interpret the result

Read reference starting-dose estimate as the output of the selected reference rule, not as proof that the medicine, formulation, route, schedule, or dose is appropriate for a particular person. The useful next step is to compare the arithmetic with the current order or label and patient-specific clinical factors.

Limitations and notes

This is a starting-dose estimate, not a prescription. Levothyroxine needs individualized titration using TSH/FT4, symptoms, age, cardiac disease, pregnancy status, interacting medicines, absorption issues, and the clinician’s target. Older adults and people with coronary disease are commonly started more cautiously than full-replacement arithmetic suggests.