Use this calculator to interpret your thyroid test results using the functional range and spot potential issues in production and/or conversion of thyroid hormone. The Thyroid produces FT4, the „4“ meaning it has 4 molecules of iodine attached to it. It then gets sent through the bloodstream and gets converted, or activated at the site of the organs that need it, by stripping it of one of its iodine molecules, making it FT3. Please note that this calculator is not intended for use in thyroid hormone replacement therapy.

An optimal result would be FT3 and FT4 both in the 45-55% range. If FT4 percentage is lower than FT3 percentage, this can point towards an issue with production of thyroid hormone. Possible causes include low intake of iodine and selenium. A lower percentage of FT3 could mean FT4 is not sufficiently converted to FT3. Consider getting a reverse-T3 blood test in this case.