Thyroid
Free T3 test cost — $9.60–$38.95
Free T3 · measured in pg/mL
The active thyroid hormone your cells actually use.
Optimal windowReference range
An assay-specific reference interval has not yet been added to this guide.
Use the interval printed beside this exact result, including its specimen, units, age/sex group and collection conditions. A range for a similarly named test may not apply.
Optimal range / clinical target
PeptideLab has not verified a separate ‘optimal’ target for this measurement. Reference intervals, diagnostic cutoffs and treatment targets answer different questions.
When Free T3 matters
Protocols and goals where this marker is worth tracking.
On TRT, HRT, GLP-1s or peptides? Use the Find tests for your goal tool to see suggested biomarkers and build your monitoring list.
Tests that include Free T3
Free T3 is included in Thyroid panel (TSH/FT3/FT4). GoodLabs and Ulta prices below cover that panel, not an individual biomarker. Test prices are shown before separate collection fees.
Tracking more than one biomarker?
Build a list to compare test and panel combinations, with one blood-draw fee in your GoodLabs estimate.
$12 blood draw per visit, added once to your order.
Collection fee is additional; not included in this test price.
* Estimated test price.
Does insurance cover Free T3 testing?
When a clinician orders Free T3 for a diagnosis or to follow a known condition, most plans cover it — and many cover routine screening as $0 preventive care for eligible adults. The catch is you need a qualifying reason and an in-network order; a “I just want to see my number” request often isn’t covered, and if you haven’t met your deductible you can end up paying the lab’s full list price anyway.
The direct-pay prices above skip insurance entirely: you pay the cash price, test on your own schedule with no doctor visit, and it’s HSA/FSA-eligible. For a single marker that’s often cheaper — and faster — than a copay plus deductible exposure.
Free T3 inside a bundle
Every compared membership/panel that includes Free T3, cheapest first. Worth it when you want several markers at once rather than a single test.
| Provider | Model | Advertised panel | Price |
|---|---|---|---|
| SiPhox Health | At-home, per-panel (selectable) | 59+ 39 biomarkers mapped | $99-124 / panel |
| Mito Health | At-cost marketplace + optional membership | 100+ 63 biomarkers mapped | Core Panel ~$198 |
| Superpower | Annual membership | 103+ 73 biomarkers mapped | $199/yr |
| Hundred | Annual membership | 160+ 74 biomarkers mapped | $199/yr |
| Function Health | Annual membership | 160+ 88 biomarkers mapped | $365/yr |
| Blueprint (Bryan Johnson) | Annual membership | 160+ 88 biomarkers mapped | $365/yr |
| Quest Health (Elite) | One-time direct-pay | 85+ 49 biomarkers mapped | $399 one-time |
| Life Extension (Elite) | One-time à-la-carte | 45+ 49 biomarkers mapped | ~$449 one-time |
| Marek Health | Annual membership | 80+ 55 biomarkers mapped | ~$495/yr |
| Thorne Advanced | One-time panel | 60+ 51 biomarkers mapped | ~$830 one-time |
| Rythm Health | At-home subscription | 24+ 22 biomarkers mapped | $79/mo |
What Free T3 is
The unbound, biologically active thyroid hormone that drives cellular metabolism, produced largely by peripheral conversion of T4. Conversion is impaired by stress, illness, or caloric restriction ('low T3 syndrome').
Why it matters for longevity & performance
Free T3 best reflects active thyroid signaling at the tissue level; low T3 associates with fatigue, though it can also be an adaptive caloric-restriction state — nuanced.
Free T3 & peptides — what to watch
If you’re running peptides, TRT or HRT, these are the compounds studied in relation to Free T3 — useful for deciding what to track. Research associations for monitoring, not medical or dosing advice. Tap one for its full profile.
Free T3 testing — frequently asked
Do I need to fast for a Free T3 test?
No. Free T3 does not require fasting — you can test any time of day.
Do I need a doctor's order to get a Free T3 test?
No. Direct-to-consumer labs (GoodLabs, Ulta, Quest and Labcorp OnDemand) include the physician order in the price — you order online and visit a draw site, no appointment with your own doctor needed.
How fast are Free T3 results?
Usually 1–3 business days after your blood draw; most results post to the lab's online portal.
What's the difference between the standard and optimal Free T3 range?
Reference intervals describe results in a reference population; they do not by themselves diagnose or exclude disease. A treatment target depends on the condition and the person. PeptideLab has not verified a separate ‘optimal’ target for this measurement. Reference intervals, diagnostic cutoffs and treatment targets answer different questions.
Which peptides affect Free T3?
Compounds studied in relation to Free T3 include HGH (Somatropin), MK-677 (Ibutamoren). These are research associations for monitoring — not medical or dosing advice.
Does insurance cover Free T3 testing?
Often, when ordered for a diagnosis; many plans cover it as preventive care at no cost for eligible adults. The direct-pay prices above let you skip insurance and test on your own schedule.
Educational guidance. Use your reporting lab’s reference interval and discuss personal targets and results with your clinician.