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Estimate conservative levothyroxine (Synthroid) adjustment from TSH bands, treatment scenario, and cardiac safety caps. Pair with TSH dose calculator for target-gap math. Educational only—not diagnosis or prescribing.
Last updated: June 5, 2026
Verify adherence and absorption before escalating. Dose changes belong to your clinician with repeat TSH in 6–8 weeks (pregnancy ~4 weeks).
Mildly above usual goal — small increment toward 0.5–2.5 band.
TSH 1.6 — at goal
100 mcg
TSH 0.5–2.5 — no change
Default: TSH 3.6 on 100 mcg
112.5 mcg
TSH 2.6–4.9 — +12.5 mcg
TSH 12.4 — under-replaced
125 mcg
TSH ≥ 10 — +25 mcg (+25% band)
TSH 0.08 — oversuppressed
112.5 mcg
TSH < 0.1 — -12.5 mcg
Pregnancy TSH 3.8
100 mcg
TSH > 3.0 (pregnancy) — +12 mcg
TSH 14.2 + CAD cap
112.5 mcg
Would be +25% but capped +12.5% — +12.5 mcg
Educational outpatient heuristics—confirm adherence before applying any % step.
| TSH band | % step | Typical action |
|---|---|---|
| TSH ≥ 10 | +25% | Markedly under-replaced — larger upward step if adherent |
| TSH 5–9.9 | +12.5% | Moderate under-replacement — common outpatient increase |
| TSH 2.6–4.9 | +6.25% | Mild elevation above goal — small increment |
| TSH 0.5–2.5 | 0% | Typical therapeutic window — maintain if clinically well |
| TSH 0.1–0.49 | −6.25% | Mild oversuppression — cautious decrease |
| TSH < 0.1 | −12.5% | Clear oversuppression — reduce and assess symptoms/bone/AF risk |
| TSH band | % step | Note |
|---|---|---|
| TSH > 3.0 | +20% | Often needs prompt increase per obstetric/endocrine plan |
| TSH 2.6–3.0 | +12.5% | Above many trimester targets — upward adjustment |
| TSH 0.1–2.5 | 0% | May be acceptable trimester-dependent — clinician judgment |
| TSH < 0.1 | −12.5% | Oversuppression — reduce with maternal/fetal risk review |
| TSH band | % step | Note |
|---|---|---|
| TSH > 0.5 | +12.5% | Below suppression goal for many DTC protocols |
| TSH 0.05–0.5 | 0% | May be at goal depending on recurrence risk tier |
| TSH < 0.05 | −12.5% | Often deeper than required — consider easing per oncology |
| Scenario | Target framing | Clinical note |
|---|---|---|
| Primary hypothyroidism | TSH ~0.5–2.5 mIU/L (lab/clinic specific) | Most adults on levothyroxine; individualized for age and comorbidity. |
| Post-thyroidectomy | Often TSH ~0.5–2.0 mIU/L | Depends on remnant tissue, cancer history, and endocrine plan. |
| Pregnancy | Trimester-specific (often <2.5, 1st tri stricter) | ATA 2017: frequent monitoring; dose needs often rise early. |
| TSH suppression | Often <0.1–0.5 mIU/L (risk-stratified) | Differentiated thyroid cancer protocols — oncology-directed. |
| Strength | Titration note |
|---|---|
| 12.5 mcg | Smallest common tablet — fine titration |
| 25 mcg | Quarter of 100 mcg strength |
| 50 mcg | Common starter/adjustment step |
| 75 mcg | Mid-range maintenance |
| 88 mcg | Brand-specific (e.g., some Synthroid) |
| 100 mcg | Typical maintenance dose anchor |
| 112 mcg | Brand-specific step |
| 125 mcg | Frequent post-titration maintenance |
| 150 mcg | Higher replacement needs |
| 175–200 mcg | High requirements — verify absorption/weight |
TSH 2.6–4.9 — Mildly above usual goal — small increment toward 0.5–2.5 band. Recheck TSH recheck in ~6–8 weeks.
| Factor | Effect | Guidance |
|---|---|---|
| Food / coffee | Reduces absorption | Empty stomach 30–60 min before breakfast; consistent timing daily. |
| Calcium / iron | Chelation — lower levels | Separate by ≥4 hours from levothyroxine. |
| PPI / sucralfate | Reduced absorption | May need higher dose or spacing — discuss with clinician. |
| Missed doses | Apparent under-replacement | Verify adherence before escalating; do not double next dose without advice. |
| Biotin supplements | Assay interference | Hold biotin before labs per lab protocol — can distort TSH/FT4. |
| Weight change | Altered requirement | Large weight shifts may need dose re-evaluation independent of TSH band. |
| Context | Interval | Why |
|---|---|---|
| Non-pregnant adult | 6–8 weeks after dose change | Levothyroxine half-life ~7 days; steady state ~4–6 weeks |
| Pregnancy | ~4 weeks (each trimester) | Rising needs and trimester-specific targets |
| New start / large change | 4–8 weeks | Earlier check if symptoms or cardiac risk |
| Elderly / CAD | 6–8+ weeks; smaller steps | Slower titration reduces angina/AF risk |
| Aspect | Thyroid medication dose (this page) | TSH dose calculator |
|---|---|---|
| Primary inputs | TSH + current mcg/day + context + safety toggles | TSH + dose + weight + explicit target TSH |
| Adjustment model | TSH-band % heuristics capped for cardiac/age | Target-gap workflow with weight-based context |
| Best for | Visit-prep: “what might my endocrine team consider?” | Exploring dose vs explicit TSH goal numerically |
| Pregnancy / suppression | Dedicated context bands built in | General hypothyroid framing |
Educational disclaimer: This calculator applies simplified TSH-band heuristics for learning and visit preparation. It does not prescribe levothyroxine, interpret full thyroid panels, or replace endocrinology, obstetric, or oncology care. Do not start, stop, or change thyroid medication based on this page alone.
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