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Quick answer
If your TSH is above your goal (for most adults, above 4.0 mIU/L), levothyroxine is usually increased by 12.5–25 mcg. If TSH is below your goal (under 0.4), it is usually decreased by 12.5–25 mcg. TSH is rechecked 6–8 weeks later. Example: TSH 5.5 on 100 mcg → 112 mcg; TSH 0.05 on 150 mcg → 125 mcg.
Enter your TSH and current dose (in mcg or mg). The calculator applies American Thyroid Association and FDA-label steps, rounds to a dose you can actually take with real Synthroid / levothyroxine tablet strengths, and adjusts the goal for pregnancy, age over 70, or thyroid cancer.
Last updated: · Sources: ATA 2014, ATA 2017, ATA 2015, FDA levothyroxine label. Guides: adjust dose by TSH · mg to mcg
ATA 2014: a TSH within the reference range is the therapeutic target for most adults. Many labs print 0.4–4.5.
Usual next step
Increase: 100 → 112 mcg/day (+12 mcg)
112 mcg = 0.112 mg/day
One 112 mcg (0.112 mg) tablet
A TSH of 5.5 is above the 0.4–4.0 mIU/L goal, which means the dose is a little low (TSH rises when thyroid hormone is too low). The usual step is 12.5–25 mcg, so 100 mcg becomes 112 mcg (0.112 mg).
Goal
0.4–4.0 mIU/L
Change
+12 mcg (+12%)
Weekly total
700 → 784 mcg
Recheck: TSH 6–8 weeks after the change (ATA 2014: 4–6 weeks)
Before changing the dose
Education only. Levothyroxine changes should be made by your prescriber, who also weighs free T4, symptoms, heart health, and pregnancy plans.
Each result comes from the calculator above, using the goal shown.
TSH 5.5 on 100 mcg
112 mcg
Goal 0.4–4.0 mIU/L · +12 mcg
TSH 8.5 on 75 mcg
100 mcg
Goal 0.4–4.0 mIU/L · +25 mcg
TSH 0.05 on 150 mcg
125 mcg
Goal 0.4–4.0 mIU/L · −25 mcg
TSH 3.2 on 100 mcg, goal 0.5–2.5
112 mcg
Goal 0.5–2.5 mIU/L · +12 mcg
Pregnant, TSH 3.4 on 88 mcg
100 mcg
Goal Below 2.5 mIU/L (lower half of trimester range) · +12 mcg
Age 78, TSH 5.2 on 75 mcg
75 mcg
Goal 0.4–6.0 mIU/L (ideal 4–6) · no change
TSH moves in the opposite direction to your thyroid hormone level. When levothyroxine is too low, the pituitary raises TSH; when it is too high, TSH drops. Examples start from 100 mcg with the standard 0.4–4.0 goal, and with the relaxed age-70+ goal (up to 6) using 12.5 mcg steps.
| TSH (mIU/L) | What it means | Usual action | Adult example | Age 70+ example |
|---|---|---|---|---|
| Below 0.1 | Overtreated (unless cancer suppression) | Decrease 12.5–25 mcg | 100 → 75 mcg | 100 → 75 mcg |
| 0.1–0.39 | Slightly overtreated | Decrease 12.5–25 mcg | 100 → 88 mcg | 100 → 88 mcg |
| 0.4–4.0 | On target | No change | 100 → 100 mcg | 100 → 100 mcg |
| 4.1–6.9 | Slightly undertreated | Increase 12.5–25 mcg | 100 → 112 mcg | 100 → 100 mcg |
| 7–10 | Undertreated | Increase 12.5–25 mcg | 100 → 125 mcg | 100 → 112 mcg |
| Above 10 | Clearly undertreated — check adherence and absorption | Increase 12.5–25 mcg | 100 → 125 mcg | 100 → 112 mcg |
There is no single "perfect" TSH. The American Thyroid Association treats any TSH within the reference range as on target for most adults, and adjusts the goal for age, pregnancy, and thyroid cancer.
| Situation | TSH goal | Source | Notes |
|---|---|---|---|
| Standard adult goal (reference range) | 0.4–4.0 mIU/L | ATA 2014 | ATA 2014: a TSH within the reference range is the therapeutic target for most adults. Many labs print 0.4–4.5. |
| Lower-normal goal (0.5–2.5) | 0.5–2.5 mIU/L | ATA 2014 (preconception); clinician preference | Used before conception (ATA 2014: below 2.5) and by clinicians who aim for the lower part of the range. Not universally endorsed for everyone. |
| Age 70–80+ (relaxed goal up to 6) | 0.4–6.0 mIU/L (ideal 4–6) | ATA 2014 | ATA 2014: reasonable to raise the target TSH to 4–6 mIU/L above age 70–80 to avoid overtreatment (atrial fibrillation, bone loss). |
| Pregnancy (already on levothyroxine) | Below 2.5 mIU/L (lower half of trimester range) | ATA 2017 | ATA 2017: keep TSH in the lower half of the trimester-specific range; if your lab has none, below 2.5 mIU/L. Check about every 4 weeks until mid-pregnancy. |
| Thyroid cancer — high risk (suppress below 0.1) | Below 0.1 mIU/L | ATA 2015 (Rec. 59) | Initial TSH suppression for high-risk differentiated thyroid cancer. Long-term goals depend on response to therapy. |
| Thyroid cancer — intermediate risk (0.1–0.5) | 0.1–0.5 mIU/L | ATA 2015 (Rec. 59) | Initial TSH goal for intermediate-risk differentiated thyroid cancer. |
| Thyroid cancer — low risk (0.5–2.0) | 0.5–2.0 mIU/L | ATA 2015 (Rec. 59) | Low-risk patients with undetectable thyroglobulin, or after lobectomy. |
| Central (pituitary) hypothyroidism | TSH not used — dose by free T4 | FDA label; ATA 2014 | In secondary or tertiary hypothyroidism TSH is unreliable. Dose is titrated to free T4 in the upper half of the reference range. |
1 mg = 1,000 mcg. Colors are the common U.S. color code; they can differ by manufacturer, so check the strength printed on the bottle.
| mcg | mg | Usual color |
|---|---|---|
| 25 mcg | 0.025 mg | Orange |
| 50 mcg | 0.05 mg | White |
| 75 mcg | 0.075 mg | Violet |
| 88 mcg | 0.088 mg | Olive |
| 100 mcg | 0.1 mg | Yellow |
| 112 mcg | 0.112 mg | Rose |
| 125 mcg | 0.125 mg | Brown (gray for some generics) |
| 137 mcg | 0.137 mg | Turquoise |
| 150 mcg | 0.15 mg | Blue |
| 175 mcg | 0.175 mg | Lilac |
| 200 mcg | 0.2 mg | Pink |
| 300 mcg | 0.3 mg | Green |
Is .25 higher than .88? Not if you mean 0.025 mg (25 mcg) — that is lower than 88 mcg. A 0.25 mg dose would be 250 mcg, which is far higher. Always compare doses in the same unit.
The nearest real tablet about 12.5 mcg away. Between 25 and 75 mcg and above 150 mcg the steps are 25 mcg, because no tablet sits in between.
| Current | One step down | One step up |
|---|---|---|
| 25 mcg (0.025 mg) | 12.5 mcg | 50 mcg |
| 50 mcg (0.05 mg) | 25 mcg | 75 mcg |
| 75 mcg (0.075 mg) | 50 mcg | 88 mcg |
| 88 mcg (0.088 mg) | 75 mcg | 100 mcg |
| 100 mcg (0.1 mg) | 88 mcg | 112 mcg |
| 112 mcg (0.112 mg) | 100 mcg | 125 mcg |
| 125 mcg (0.125 mg) | 112 mcg | 137 mcg |
| 137 mcg (0.137 mg) | 125 mcg | 150 mcg |
| 150 mcg (0.15 mg) | 137 mcg | 175 mcg |
| 175 mcg (0.175 mg) | 150 mcg | 200 mcg |
| 200 mcg (0.2 mg) | 175 mcg | 225 mcg |
| Who | Typical start | Source |
|---|---|---|
| Adult under 50–60, no heart disease, TSH markedly high | Full dose ≈ 1.6 mcg/kg/day (0.73 mcg/lb) | ATA 2014; FDA label |
| Mild hypothyroidism (TSH ≤ 10) | 25–50 mcg/day | ATA 2014 |
| Coronary artery disease | 12.5–25 mcg/day, slow increases | ATA 2014 |
| Older adults or atrial-fibrillation risk | Below 1.6 mcg/kg; titrate every 6–8 weeks | FDA label |
| New overt hypothyroidism in pregnancy (TSH ≥ 10) | 1.6 mcg/kg/day, TSH every 4 weeks | FDA label |
| Weight | 1.6 mcg/kg | Nearest tablet |
|---|---|---|
| 100 lb (45.4 kg) | 73 mcg | 75 mcg |
| 120 lb (54.4 kg) | 87 mcg | 88 mcg |
| 140 lb (63.5 kg) | 102 mcg | 100 mcg |
| 160 lb (72.6 kg) | 116 mcg | 112 mcg |
| 175 lb (79.4 kg) | 127 mcg | 125 mcg |
| 200 lb (90.7 kg) | 145 mcg | 150 mcg |
| 225 lb (102.1 kg) | 163 mcg | 175 mcg |
| 250 lb (113.4 kg) | 181 mcg | 175 mcg |
Full doses suit people with little or no thyroid function and no heart disease. Many people need less.
| When | Interval | Why |
|---|---|---|
| After any dose change (adults) | 6–8 weeks (ATA: 4–6) | Levothyroxine half-life is about 7 days; TSH takes ~6 weeks to settle |
| Heart disease or AF risk | Titrate every 6–8 weeks | Slower increases avoid heart strain |
| Pregnancy | Every 4 weeks to mid-pregnancy, then ~30 weeks | Needs rise by 25–50% in many women |
| After delivery | Return to pre-pregnancy dose; TSH at ~6 weeks | Postpartum needs return to baseline |
| Stable dose | Every 6–12 months | Routine monitoring |
| Factor | What to do |
|---|---|
| Food and coffee | Take on an empty stomach 30–60 minutes before breakfast with water |
| Calcium, iron, antacids, prenatal vitamins | Separate by at least 4 hours |
| Bile-acid binders (cholestyramine, colesevelam) | Take levothyroxine at least 4 hours before |
| PPIs, celiac disease, H. pylori, bariatric surgery | Can lower absorption — may need a higher dose |
| Estrogen, pregnancy | Raise binding protein and dose needs |
| Biotin supplements | Can distort TSH lab results — ask about pausing before tests |
Looking for scenario-based titration with cardiac caps? Try the thyroid medication dose calculator.
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