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Estimate conservative levothyroxine (Synthroid) changes from TSH bands, your explicit target TSH, and optional weight-based reference (1.6 mcg/kg). Compare with thyroid medication dose calculator for scenario-band caps. Educational only—not prescribing.
Last updated: June 5, 2026
Verify adherence and absorption before escalating. Recheck 6–8 weeks after changes (pregnancy ~4 weeks).
Shows 1.6 mcg/kg reference — not auto-dose
Suggested dose
112.5 mcg
Increase from 100 mcg to 112.5 mcg
Dose change
+12.5%
TSH gap vs target
+2
TSH above target 1.5 — mild under-replacement if adherent.
Target range (0.5–2.5 mIU/L)
Weight-based reference (~1.6 mcg/kg): 112.5 mcg/day
TSH 1.5 — at target
100 mcg
No change — gap 0
Default: TSH 3.5 on 100 mcg
112.5 mcg
+12.5 mcg — target 1.5
TSH 6.5 on 75 mcg
100 mcg
+25% band — adherence check first
TSH 0.05 — oversuppressed
137.5 mcg
-12.5 mcg change
Pregnancy TSH 3.2
125 mcg
~4-week recheck
Cancer suppression TSH 0.08
175 mcg
Maintain — at suppression goal
Educational outpatient heuristics — confirm adherence before applying % steps.
| TSH band | % step | Action |
|---|---|---|
| TSH < 0.1 | −12.5% | Clear oversuppression — reduce unless intentional cancer suppression |
| TSH 0.1–0.49 | −6.25% | Mild low TSH — small decrease (maintain if cancer suppression goal) |
| TSH 0.5–2.5 | 0% | Typical therapeutic window for primary hypothyroidism |
| TSH 2.6–5.0 | +12.5% | Mild under-replacement — common outpatient step |
| TSH 5.1–10.0 | +25% | Moderate under-replacement — verify adherence first |
| TSH > 10 | +25% | Marked elevation — adherence/absorption review + increase |
| Condition | Target framing | Default target | Note |
|---|---|---|---|
| Primary hypothyroidism | TSH ~0.5–2.5 mIU/L | 1.5 | Most adults on levothyroxine replacement. |
| Pregnancy | 1st tri ~0.1–2.5; 2nd–3rd ~0.2–3.0 | 2.0 | ATA 2017 — recheck ~4 weeks; dose often rises 30–50%. |
| Thyroid cancer suppression | Often <0.1–0.5 by risk tier | 0.1 | Oncology-directed — not standard replacement goals. |
| Subclinical hypothyroidism | 0.5–2.5 if treated | 1.5 | Treat when TSH >10 or symptoms; 4–10 controversial. |
| Elderly | Some accept ~4–6 mIU/L | 3.0 | Avoid overtreatment — AF and bone loss risk. |
| TSH band | % step | Note |
|---|---|---|
| TSH > 3.0 | +20% | Often needs prompt increase per obstetric plan |
| TSH 2.6–3.0 | +12.5% | Above many trimester targets |
| TSH 0.1–2.5 | 0% | May be acceptable trimester-dependent |
| TSH < 0.1 | −12.5% | Oversuppression — maternal/fetal risk review |
| Population | Dose | Example |
|---|---|---|
| Young healthy adult | ~1.6 mcg/kg/day | 70 kg → ~112 mcg |
| Elderly or CAD | 12.5–25 mcg start, slow titration | Increase q6–8 weeks |
| Pregnancy (new diagnosis) | ~2.0–2.4 mcg/kg/day | Often 30–50% above pre-pregnancy |
| Severe longstanding hypo | 25–50 mcg start | Avoid cardiac stress from rapid rise |
TSH 2.6–5.0 — TSH above target 1.5 — mild under-replacement if adherent. Recheck in 6–8 weeks.
| Factor | Effect | Guidance |
|---|---|---|
| Food / coffee | ↓ absorption 20–30% | Empty stomach 30–60 min before breakfast |
| Calcium / iron | Chelation | Separate ≥4 hours |
| PPI / sucralfate | ↓ absorption | May need higher dose — clinician review |
| Missed doses | Apparent under-replacement | Verify adherence before +25% jumps |
| Biotin | Assay interference | Hold before TSH draw per lab protocol |
| Context | Interval | Why |
|---|---|---|
| After dose change (adult) | 6–8 weeks | Levothyroxine t½ ~7 days; steady state ~4–6 weeks |
| Pregnancy | ~4 weeks each trimester | Rising requirements and trimester targets |
| Stable on dose | 6–12 months | Routine monitoring if asymptomatic |
| TSH > 10 / symptomatic | 4–6 weeks after change | Closer follow-up for marked deviation |
| Strength | Note |
|---|---|
| 12.5 mcg | Fine titration increment |
| 25 / 50 mcg | Common starter strengths |
| 75 / 88 / 100 mcg | Maintenance range |
| 112 / 125 / 137 mcg | Post-titration steps |
| 150–200 mcg | Higher requirements |
| Aspect | TSH dose (this page) | Thyroid medication dose |
|---|---|---|
| Primary inputs | TSH + dose + explicit target TSH + weight + condition | TSH + dose + context toggles (cardiac/age) without target number |
| Adjustment model | TSH bands + target-gap framing + weight reference (1.6 mcg/kg) | TSH-band % with pregnancy/suppression built-in |
| Best for | “My goal TSH is 1.5 — how much to move dose?” | Scenario-based bands with safety caps |
Educational disclaimer: This calculator applies simplified TSH-band heuristics with target-gap framing for learning and visit preparation. It does not prescribe levothyroxine, interpret full thyroid panels, or replace endocrinology care. Do not start, stop, or change thyroid medication based on this page alone.
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