Armour Thyroid & NDT Dosage Calculator

This calculator gives you a weight-based starting dose of natural desiccated thyroid (NDT) for Armour Thyroid, NP Thyroid, or compounded NDT. It uses my clinical conversion math (1 grain NDT = 75 mcg T4 equivalent, with T3 valued at 3x T4 potency), which gives you more NDT than the conventional pharmaceutical chart, because the conventional chart underdoses patients^[1]. The calc also gives you a 4-week titration schedule because the T3 in NDT is immediately active, and dropping a full dose on day one can cause palpitations, anxiety, or jitters^[2].

Here’s how to use it:

Pick a conversion method (the default is my recommended one), pick the clinical scenario that fits you, enter your weight, height, age, and sex, pick which NDT brand you’ll be taking, and flag any modifiers (heart condition, ideal body weight). The calculator returns your starting dose in grains and milligrams, your full replacement target, the T4 and T3 component breakdown, and a titration schedule from week 1 through week 8.

Note: This calculator is a clinical tool, not a prescription. Don’t start or change thyroid medication based on the results without your doctor. Heart condition, age 65 or older, pregnancy, and adrenal issues all change how this dose should be approached.

Written and medically reviewed by Dr. Westin Childs, D.O. Last reviewed: April 25, 2026.

How to Use This Calculator

Step #1: Pick Your Conversion Method

Three options. Dr. Childs Recommended is the default and the one I use clinically. The Updated 2013 Study method comes from a randomized trial that compared NDT to levothyroxine. The Conventional method is the standard pharmaceutical chart taught in medical school.

The math under each method differs in how potent it considers NDT relative to T4. My method (Childs) treats 1 grain of NDT as equivalent to 75 mcg of T4 with T3 valued at 3x potency. The Updated 2013 method uses 88 mcg per grain. The Conventional method uses 100 mcg per grain^[1]. The conventional chart consistently underdoses patients switching to NDT, which is why I use a different number.

If you’re not sure which method to pick, leave it on Dr. Childs Recommended. The other two are there for transparency and for patients whose doctors are working off the conventional chart.

Step #2: Pick Your Clinical Scenario

Five options. New thyroid diagnosis is the default. The other four (post-thyroidectomy benign, post-thyroidectomy cancer, subclinical hypothyroidism, new pregnancy) each adjust the math for the higher or lower replacement need that comes with that scenario^[2].

Post-thyroidectomy patients need the highest doses because they have zero remaining native thyroid function. Cancer patients on TSH suppression need slightly more than that to keep TSH below 0.5 (or below 0.1 for higher-risk cases). Subclinical hypothyroidism needs the lowest dose because there’s still some residual thyroid function. Pregnancy needs the highest multiplier because thyroid hormone demand increases 30 to 50 percent during pregnancy^[10].

If you’re pregnant, the calculator will still output a number, but you’ll see a banner explaining that most doctors recommend T4 monotherapy during pregnancy because maternal T3 doesn’t cross the placenta as efficiently. NDT can still work in pregnancy with physician supervision.

Step #3: Enter Your Weight, Height, Age, and Sex

Weight is required and is the main driver of your dose. Height, age, and sex sharpen the calculation in two ways. Height plus weight gives a BMI; if your BMI is 30 or higher, the calculator switches to ideal body weight automatically (using the Devine formula) so the dose lands on muscle mass instead of total body weight. Age 65 or older triggers a more conservative starting dose and longer titration.

Use the toggles next to weight and height if you prefer kilograms or centimeters. Either works. Sex (at birth) is used for the ideal body weight calculation only.

Step #4: Pick Your NDT Brand

Two commercial brands are still available in the US: Armour Thyroid and NP Thyroid. Both contain the same hormone content per grain (38 mcg T4 plus 9 mcg T3). The difference is in which fillers and binders are used and which manufacturer makes them.

Armour Thyroid and NP Thyroid both come in 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, and 5 grain strengths. Pick the brand your prescriber will write or your pharmacy stocks. The calculator rounds your calculated dose to the nearest available tablet strength.

Step #5: Flag Any Modifiers That Apply

Two checkboxes. Heart condition (heart attack, heart disease, heart failure, angina, or arrhythmia) caps both your starting dose and your full target at lower numbers because the T3 in NDT raises cardiac demand more than T4 alone. Use ideal body weight is auto-checked if your BMI is 30 or higher; you don’t usually need to touch this manually.

The cardiac cap is a hard ceiling. If your weight-based calculated dose was 2 grains and you check the cardiac box, the calculator drops your full target to 1 grain and your starting dose to 0.25 grain. The titration also doubles to 4 weeks instead of 2 weeks before stepping up. Cardiology supervision is essential during titration.

Age 65 or older isn’t a manual checkbox; the calculator picks it up automatically from the age field. Same conservative protocol applies: lower starting dose, lower full target (1.5 grains max), 4-week titration.

Understanding Your Results

Your Starting Dose

The big number at the top of your results is your week 1 starting dose in grains. It’s half of your full replacement target. You stay at this dose for the first week, then step up to the full target in week 2 (or week 4 if you’re cardiac or elderly). The reason to start at half is to let your body adjust to the T3 component without triggering palpitations, jitters, or anxiety.

Take your dose in the morning on an empty stomach, at least 30 to 60 minutes before food, coffee, calcium, or iron. Food and certain supplements reduce thyroid medication absorption by up to 30 percent^[5]. Some patients prefer nighttime dosing (3 hours after the last meal); both windows work as long as you’re consistent.

Your Full Replacement Target

The full replacement target is what your dose should land on by week 2 (or week 4 for cardiac and elderly patients). It’s the weight-based calculation: your weight in kilograms multiplied by the scenario multiplier (1.6 to 2.2 mcg of T4 equivalent per kilogram), divided by your selected method’s grain-to-T4 conversion (75 mcg per grain for Childs, 88 for Updated 2013, 100 for Conventional)^[1].

For most adults, the full replacement target lands between 1 and 3 grains per day. Anything below 1 grain is a low-replacement dose (typical for subclinical hypothyroidism or partial replacement). Anything above 3 grains is uncommon and usually only seen in post-thyroidectomy patients or pregnancy.

The full target is rounded to the nearest commercially available tablet strength for your selected brand. If your raw calculation lands at 1.74 grains and the nearest tablet is 1.5 grains, that’s what shows. You can always adjust later based on your labs and how you feel.

T4 and T3 Component Breakdown

Each grain of NDT contains 38 mcg of T4 and 9 mcg of T3^[3]. The component breakdown shows you exactly how much of each hormone you’re getting at your full target dose. For example, a 1.5 grain target gives you 57 mcg of T4 and 13.5 mcg of T3 per day. A 2 grain target gives 76 mcg of T4 and 18 mcg of T3.

This matters because NDT patients often want to compare their hormone load to a T4-only dose. A patient on 1.5 grains of NDT is getting roughly equivalent to 100 to 125 mcg of T4 (using my method’s math), but with the T3 component layered on top. That’s the appeal of NDT for patients with poor T4-to-T3 conversion: you bypass the conversion issue and get T3 directly^[1].

The Titration Plan

The titration plan walks you through week 1, week 2 (or week 4), and the lab recheck at week 6 to 8 (or week 8 to 10 for cardiac and elderly patients). Standard patients titrate fast: half dose week 1, full target week 2 onward. Cardiac and elderly patients titrate slow: half dose for 4 weeks, full target from week 4 on.

If you experience anxiety, jitters, heart palpitations, or insomnia during titration, slow down. Stay at the lower dose another 1 to 2 weeks before stepping up. T3 has a faster onset than T4, so feeling a stimulant-like response early is common but should be temporary. If symptoms persist past week 2 of full dose, the dose is too high for you and needs to come down^[1].

Lab recheck at week 6 to 8 includes TSH, Free T4, Free T3, and Reverse T3. Most patients end up needing 0.25 to 0.5 grain adjustments based on their labs. The final stable dose typically sits between 1 and 3 grains depending on weight and clinical scenario.

When Your Dose Gets Capped

Three flags trigger safety caps. Heart condition checked, age 65 or older, or both stacked. Each cap lowers both your starting dose and your full replacement target.

Heart condition alone caps starting dose at 0.25 grain and full target at 1 grain. Age 65 or older alone caps starting dose at 0.5 grain and full target at 1.5 grains. Both stacked (cardiac plus elderly) caps starting dose at 0.25 grain and full target at 1 grain. Titration also doubles from 2 weeks to 4 weeks for any of these flags.

The reason for capping the full target (not just the starting dose) is that T3 raises cardiovascular demand more than T4 alone. A 70-year-old cardiac patient titrating to a full weight-based 2 grain dose is at meaningful risk for atrial fibrillation, chest pain, or worsening heart failure^[2]. Capping at 1 grain gives you a meaningful therapeutic dose without that risk. You can titrate beyond the cap with cardiology supervision if labs and symptoms support it, but the calc won’t suggest doing that automatically.

NDT Dosage by Weight Reference Table

The table below shows weight-based starting doses and full replacement targets for new thyroid diagnosis using my Dr. Childs Recommended method. The starting dose is what you take in week 1; the full target is what you titrate to in week 2 and beyond. Doses are rounded to the nearest commercially available tablet strength for Armour Thyroid (NP Thyroid uses the same strengths)^[3].

Weight (lb / kg)	Starting Dose (Week 1)	Full Target (Week 2+)	T4 + T3 Components (Full Dose)
100 lb / 45 kg	0.5 grain (30 mg)	1 grain (60 mg)	38 mcg T4 + 9 mcg T3
120 lb / 54 kg	0.5 grain (30 mg)	1 grain (60 mg)	38 mcg T4 + 9 mcg T3
140 lb / 64 kg	0.75 grain (45 mg)	1.5 grain (90 mg)	57 mcg T4 + 13.5 mcg T3
160 lb / 73 kg	0.75 grain (45 mg)	1.5 grain (90 mg)	57 mcg T4 + 13.5 mcg T3
180 lb / 82 kg	0.75 grain (45 mg)	1.5 grain (90 mg)	57 mcg T4 + 13.5 mcg T3
200 lb / 91 kg	1 grain (60 mg)	2 grains (120 mg)	76 mcg T4 + 18 mcg T3
220 lb / 100 kg	1 grain (60 mg)	2 grains (120 mg)	76 mcg T4 + 18 mcg T3
240 lb / 109 kg	1 grain (60 mg)	2 grains (120 mg)	76 mcg T4 + 18 mcg T3

These doses use actual body weight. If your BMI is 30 or higher, the calculator switches to ideal body weight automatically, which gives a slightly lower dose because thyroid hormone is used by lean tissue, not fat tissue^[2]. Doses for post-thyroidectomy, thyroid cancer, and pregnancy run higher than this table because the multiplier is higher (1.7, 2.0, and 2.2 mcg/kg respectively, vs 1.6 for new diagnosis).

Want to switch from Synthroid or another T4 medication to NDT instead of starting fresh? Use the Thyroid Medication Conversion Calculator.

Want to know whether your labs are in the optimal range after starting NDT? Use the Optimal Thyroid Lab Test Calculator.

Want to check your T4 to T3 conversion before starting NDT? Use the Reverse T3 Ratio Calculator.

Frequently Asked Questions

1 grain of Armour Thyroid equals 60 mg. So 0.5 grain is 30 mg, 1.5 grains is 90 mg, 2 grains is 120 mg, and 3 grains is 180 mg^[3]. The grain unit is a holdover from when desiccated thyroid was first made (early 1900s) when pharmacy used grains as the standard weight unit. The mg measurement is what your prescription bottle and pharmacy label use today, but the tablets are still labeled in grains because that’s what doctors and patients are used to.

Same conversion applies to NP Thyroid: 1 grain equals 60 mg in both brands.

1 grain of Armour Thyroid contains 38 mcg of T4 and 9 mcg of T3^[3]. The ratio matches what a healthy thyroid gland naturally secretes (approximately 80 percent T4 and 20 percent T3 by mass), which is why NDT works well for many patients with hypothyroidism.

Multiply by your dose to get your total daily hormone load. A 1.5 grain dose gives 57 mcg T4 plus 13.5 mcg T3. A 2 grain dose gives 76 mcg T4 plus 18 mcg T3. NP Thyroid has the same per-grain content as Armour, so the math is identical regardless of brand.

For most healthy adults with newly diagnosed hypothyroidism, a good starting dose of Armour Thyroid is 0.5 to 0.75 grain (30 to 45 mg) per day for the first week, then stepping up to 1 to 1.5 grains by week 2^[2]. The exact starting dose depends on your weight, your clinical scenario (new diagnosis, post-thyroidectomy, subclinical, pregnancy), and any cardiac or age-related modifiers.

Patients with a heart condition or age 65 or older should start at 0.25 grain (15 mg) and titrate over 4 weeks instead of 2. The reason is that the T3 in Armour Thyroid raises cardiac demand more than T4-only medications, so a slower introduction reduces the risk of palpitations or arrhythmia.

Run your specific weight through the calculator above for your exact starting dose.

Armour Thyroid is available in 9 tablet strengths: 0.25 grain (15 mg), 0.5 grain (30 mg), 0.75 grain (45 mg), 1 grain (60 mg), 1.5 grains (90 mg), 2 grains (120 mg), 3 grains (180 mg), 4 grains (240 mg), and 5 grains (300 mg). NP Thyroid offers the same range.

Most adult patients end up on 1 to 3 grains per day as their stable dose. Patients on full thyroid replacement after thyroidectomy sometimes need higher doses (3 to 4 grains). Subclinical hypothyroidism patients may stabilize on 0.5 to 1 grain. Outside of those ranges, dosing usually means there’s another issue (absorption, drug interactions, or wrong diagnosis) worth investigating.

Armour Thyroid is dosed at approximately 1.6 mcg of T4-equivalent per kilogram of body weight per day for new diagnosis, divided by 75 mcg per grain (the conversion ratio I use clinically). For a 70 kg adult, that’s 70 × 1.6 = 112 mcg of T4-equivalent, divided by 75 = 1.5 grains per day as the full replacement target^[1]^[2].

The starting dose is half of that (about 0.75 grain for a 70 kg adult) for the first week, then full target from week 2. Patients with BMI 30 or higher should use ideal body weight for the calculation, not actual weight, because thyroid hormone is used by lean tissue and not fat tissue. The calculator handles this automatically.

Post-thyroidectomy patients use a slightly higher multiplier (1.7 to 2.0 mcg/kg). Pregnancy uses 2.2 mcg/kg. Subclinical hypothyroidism uses 1.1 mcg/kg.

The most common side effects of too much Armour Thyroid are heart palpitations, jitters, anxiety, insomnia, heat intolerance, a racing heart rate, and tremors. These are signs of hyperthyroidism (too much thyroid hormone). Less common but more serious effects include atrial fibrillation, chest pain, and bone density loss with chronic over-replacement^[2].

The T3 component in Armour Thyroid causes faster and stronger symptoms when over-replaced compared to T4-only medications, because T3 is the active hormone. If you start NDT and feel jittery or anxious within a few days, your dose is likely too high or you titrated too fast. Drop back to your previous dose and titrate up more slowly under physician supervision.

Lab signs of over-replacement: TSH below 0.1 (in non-suppression patients), Free T3 above the top of the reference range, or Free T4 above the top of the reference range.

The T3 component in Armour Thyroid is biologically active within 1 to 2 hours of taking it, but symptom improvement takes longer. Most patients notice better energy, clearer thinking, and warmer extremities within the first 1 to 2 weeks of starting Armour. Weight loss, hair regrowth, and full mood improvement usually take 6 to 12 weeks^[1].

If you don’t feel any change by week 4, your dose is probably too low. Recheck labs at week 6 to 8 and consider a dose increase based on the results. If you feel worse instead of better (palpitations, jitters, anxiety, insomnia), your dose is too high or you titrated too fast. Drop back to the starting dose and re-titrate more slowly.

Yes, you can switch from levothyroxine to Armour Thyroid. The conversion is approximately 100 mcg of levothyroxine equals 1 grain of Armour using the conventional pharmaceutical chart, but I use a different ratio (75 mcg per grain) clinically because the conventional chart consistently underdoses patients on the switch^[1].

For the actual conversion math from your current levothyroxine dose to your equivalent Armour Thyroid dose, use the Thyroid Medication Conversion Calculator. That calc handles the conversion in both directions and lets you pick between three conversion methods.

You’ll need a prescription from your doctor to make the switch. Most conventional endocrinologists are reluctant to prescribe NDT because levothyroxine is the standard of care. Functional medicine doctors and integrative physicians are more comfortable with NDT. You may need to switch prescribers if your current doctor won’t consider it.

Most patients do fine on once-daily Armour Thyroid dosing in the morning. The T4 component has a 7-day half-life and the T3 component has a 24-hour half-life, which together gives reasonably stable hormone levels through the day on a single morning dose^[7].

Split the dose twice daily (morning and early afternoon) if you feel a distinct afternoon energy crash on once-daily dosing. The T3 portion peaks within 2 to 3 hours and tapers over the rest of the day; some patients feel that taper as fatigue or brain fog by mid-afternoon. Splitting smooths the hormone curve. The total daily dose stays the same, just divided across two times.

Don’t take the second dose late in the evening because the T3 component can cause insomnia. The early afternoon split (around 1 to 2 PM) gives the T3 enough time to clear before bedtime.

Take Armour Thyroid in the morning on an empty stomach, at least 30 to 60 minutes before food, coffee, calcium, iron, or any other supplements. Food in the stomach reduces absorption by up to 30 percent^[5]. Coffee specifically interferes with absorption even more than food does and should be timed at least 60 minutes after the dose.

If morning doesn’t work for you, nighttime dosing is a valid alternative. Take the dose at least 3 hours after your last meal, just before bed. Either window works as long as you stay consistent with the timing day to day.

Other absorption blockers to time away from your dose by at least 4 hours: calcium supplements, iron supplements, multivitamins containing iron or calcium, antacids, proton pump inhibitors (PPIs), and bile acid binders. These can reduce absorption by 30 to 50 percent if taken close together.

References

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Jonklaas J, Bianco AC, Bauer AJ, et al. Guidelines for the treatment of hypothyroidism: prepared by the American Thyroid Association task force on thyroid hormone replacement. Thyroid. 2014;24(12):1670-1751. View on PubMed
Shahid MA, Ashraf MA, Sharma S. Physiology, Thyroid Hormone. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023. View on NCBI
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Escobar-Morreale HF, Botella-Carretero JI, Escobar del Rey F, Morreale de Escobar G. Treatment of hypothyroidism with combinations of levothyroxine plus liothyronine. Journal of Clinical Endocrinology and Metabolism. 2005;90(8):4946-4954. View on PubMed
Alexander EK, Pearce EN, Brent GA, et al. 2017 Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and the postpartum. Thyroid. 2017;27(3):315-389. View on PubMed
Haugen BR, Alexander EK, Bible KC, et al. 2015 American Thyroid Association management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer. Thyroid. 2016;26(1):1-133. View on PubMed
Peterson SJ, Cappola AR, Castro MR, et al. An online survey of hypothyroid patients demonstrates prominent dissatisfaction. Thyroid. 2018;28(6):707-721. View on PubMed