Thyroid
Free T4 test cost — $9.60–$38.95
Free T4 · measured in ng/dL
Your thyroid hormone reservoir, ready for conversion.
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 T4 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 T4
Free T4 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 T4 testing?
When a clinician orders Free T4 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 T4 inside a bundle
Every compared membership/panel that includes Free T4, 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 |
| OneTwenty | Annual membership | 85+ 51 biomarkers mapped | $499/yr |
| Thorne Advanced | One-time panel | 60+ 51 biomarkers mapped | ~$830 one-time |
| Lifeforce | Subscription + diagnostic | 51+ 49 biomarkers mapped | ~$2,137/yr |
What Free T4 is
The unbound, available fraction of thyroxine (T4) — the main thyroid-hormone reservoir converted peripherally into active T3. Not bound to carrier proteins, so it reflects true availability.
Why it matters for longevity & performance
Adequate thyroid hormone supports metabolism and cognition; free T4 helps distinguish central from primary thyroid issues alongside TSH.
Free T4 & peptides — what to watch
If you’re running peptides, TRT or HRT, these are the compounds studied in relation to Free T4 — useful for deciding what to track. Research associations for monitoring, not medical or dosing advice. Tap one for its full profile.
Free T4 testing — frequently asked
Do I need to fast for a Free T4 test?
No. Free T4 does not require fasting — you can test any time of day.
Do I need a doctor's order to get a Free T4 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 T4 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 T4 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 T4?
Compounds studied in relation to Free T4 include HGH (Somatropin), Tesamorelin. These are research associations for monitoring — not medical or dosing advice.
Does insurance cover Free T4 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.