Levothyroxine Dose Adjustment from TSH Calculator
Levothyroxine Dose Adjustment from TSH Calculator
Adjust an established levothyroxine dose against the current TSH using the label’s 12.5 and 25 µg increments, with the target range for the clinical situation.
Levothyroxine dose adjustment
Dose + TSH + target → adjusted doseAn adult on 100 µg of levothyroxine daily for the past three months, TSH 7.4 mIU/L, free T4 at the lower end of the range, standard adult target, adjusting in 25 µg steps
What this calculates, and what it cannot
- 12.5–25 µg
- the approved labelling: “adjust the dose by 12.5 mcg to 25 mcg increments every 4 to 6 weeks until the patient is clinically euthyroid”
- Which increment
- not published. No guideline maps the step size to the distance from target, so this page asks rather than guesses
- Standard target
- TSH 0.4–4.0 mIU/L — the ATA’s stated therapeutic target for replacement
- Pregnancy target
- TSH below 2.5 mIU/L when a trimester-specific range is not available
- Older adults
- TSH around 1–5 mIU/L is acceptable over 70–75 years (ETA recommendation 22)
- Re-check interval
- 6 weeks to steady state (ATA); 4 weeks in pregnancy (label)
Worked example
An adult on 100 µg of levothyroxine daily for the past three months, TSH 7.4 mIU/L, free T4 at the lower end of the range, standard adult target, adjusting in 25 µg steps
Standard adult target → TSH 0.4–4.0 mIU/L (ATA's stated therapeutic target)
TSH 7.4 mIU/L is above 4.0 → under-replaced
One increment of 25 µg added to 100 µg → 125.0 µg daily, a rise of 25.0%
Recheck the TSH no sooner than 6 weeks — the ATA gives steady state as reached "in 6 weeks (approximately five to six half-lives)"
And before accepting the increase, check the tablet is being taken fasting and four hours away from calcium, iron and proton pump inhibitors
The target depends on who the patient is
| Situation | TSH target | Source |
|---|---|---|
| Standard adult replacement | 0.4 – 4.0 mIU/L | ATA 2014: “a value within the reference range (0.4–4.0 mIU/L) should be considered the therapeutic target” |
| Pregnancy, or trying to conceive | Lower limit of the range to 2.5 mIU/L | ATA: “adjusted to target a TSH level between the lower limit of the reference range and 2.5 mU/L”, with a trimester-specific range preferred where one exists |
| First trimester, where only a standard range is available | Upper reference limit about 4.0 mIU/L | ATA 2017 pregnancy guideline: the upper reference range “is reduced by approximately 0.5 mU/L”, giving “a TSH upper reference limit of 4.0 mU/L” |
| Age over 70 – 75 | About 1 – 5 mIU/L | ETA 2013 recommendation 22: “for older patients (>70–75 years), a higher treatment target for serum TSH (around 1–5 mU/l) is acceptable” |
| Age over 80 – 85, TSH ≤10 and untreated | Usually no treatment at all | ETA 2013 recommendation 15: a “wait-and-see strategy, generally avoiding hormonal treatment” |
| After differentiated thyroid cancer | No numeric target is published | The 2025 ATA guideline “do not provide target TSH ranges for any patients, but simply state that TSH should be maintained ‘below’ or ‘within’ the reference range” |
Absorption: the commonest reason a TSH will not settle
| Interaction | What to do |
|---|---|
| Food of any kind | Take on an empty stomach, half an hour to an hour before breakfast. Taking it with breakfast reduces absorption substantially |
| Coffee | Espresso and coffee taken with the tablet impair absorption. Separate them, or take the tablet at bedtime instead |
| Calcium salts | Separate by at least 4 hours — the label’s own instruction for interacting drugs |
| Iron salts | Separate by at least 4 hours |
| Proton pump inhibitors | Reduced gastric acid impairs dissolution of the tablet. Reassess the TSH after a PPI is started or stopped |
| Soy products, high-fibre diets | Separate from the dose; a change in diet can shift the TSH without any change in prescription |
| Coeliac disease, atrophic gastritis, bariatric surgery | Malabsorption, not non-adherence. A requirement far above 1.6 µg/kg should prompt the question |
Which levothyroxine page answers which question
| Question | Page |
|---|---|
| What dose should this patient start on? | Levothyroxine dose calculator — weight-based initiation, and the reasons to start lower |
| The TSH is off target on an established dose. Now what? | This page |
| How much liothyronine is equivalent to this much levothyroxine? | Levothyroxine to liothyronine converter |
| The TSH is in range but the free T3 looks low | FT3:FT4 ratio calculator — and read its warning about treating a ratio |
| What is this TSH in other units? | TSH unit converter |
| Is the thyroid overactive rather than under-treated? | Burch-Wartofsky score for suspected thyroid storm |
The increment is in the label, not in the guideline — and the six weeks is not negotiable
Adjusting an established levothyroxine dose is a smaller problem than starting one, and it has an awkward feature: the guidelines that set the target do not tell you the size of the step. The American Thyroid Association’s 2014 treatment guideline gives the target — “a value within the reference range (0.4–4.0 mIU/L) should be considered the therapeutic target” — and the timescale, “steady-state levels of T4 and TSH are generally achieved in 6 weeks (approximately five to six half-lives)”, and then leaves the increment to the prescriber. The number everyone uses comes from the approved labelling instead, which says to “adjust the dose by 12.5 mcg to 25 mcg increments every 4 to 6 weeks until the patient is clinically euthyroid”. That is where 12.5 and 25 µg come from, and it is also why this page asks which of the two you are using rather than choosing for you: no source maps the step size onto how far the TSH is from target, so any calculator that picks one automatically has invented a threshold.
The six-week interval is the part most worth defending. Thyroxine has a half-life of about a week, so five or six of them have to pass before the concentration stops moving, and the pituitary’s TSH output lags behind that. A TSH drawn at three weeks after a dose change is reporting a system still in transit, and acting on it produces the familiar pattern of a patient whose dose is adjusted every month and never settles. The label’s shorter figure of four weeks and the ATA’s six are both on this page because they do not agree; the calculator prints six outside pregnancy, on the basis that the longer figure is the one that reflects steady state. In pregnancy the interval genuinely is shorter — the label says to “measure TSH every 4 weeks” — because requirement rises through the first trimester and waiting six weeks means chasing it.
The target is not one number. In pregnancy the ATA’s advice is to aim between the lower limit of the reference range and 2.5 mIU/L, with a trimester-specific range used where the laboratory has one; the 2017 pregnancy guideline notes that the first-trimester upper reference limit works out at about 4.0 mIU/L for a typical patient, which is lower than the non-pregnant limit. In older patients the target goes the other way: the European Thyroid Association’s 2013 guideline says that “for older patients (>70–75 years), a higher treatment target for serum TSH (around 1–5 mU/l) is acceptable”, and that the oldest old with a TSH of 10 mIU/L or less should generally not be treated at all. After thyroid cancer there is now no numeric target to aim at — the 2025 ATA guideline withdrew the risk-stratified figures the 2015 guideline gave and no longer recommends complete suppression — which is why the selector on this page has three options and not four.
Finally, the question to ask before increasing anything. Before increasing an established dose, ask how it is being taken. Levothyroxine should go down on an empty stomach, half an hour to an hour before breakfast, and at least four hours away from calcium, iron, proton pump inhibitors and soy. Poor absorption is a commoner cause of a stubborn TSH than an inadequate dose. Calcium and iron have to be separated by four hours, a proton pump inhibitor changes tablet dissolution, and coffee taken with the dose is enough to matter. A TSH that has drifted up on a dose that used to work is far more often a change in how the tablet is being taken — or a new PPI, or a new calcium supplement, or a pregnancy — than a thyroid that has deteriorated. And a requirement well above about 1.6 µg/kg should raise malabsorption, coeliac disease or non-adherence rather than prompting another increment. The dose shown above is one step in one direction; it is a prompt for a conversation and a repeat test, not a prescription. This supports a clinician’s judgement rather than replacing it. It is arithmetic on the figures entered, and it knows nothing about the patient in front of you.
Frequently asked questions
How much should a levothyroxine dose be adjusted by?
The approved labelling gives increments of 12.5 to 25 µg. It does not say which to use when, and no guideline maps the step size to how far the TSH sits from target — that choice is clinical judgement, weighing the size of the gap against the patient’s age and cardiac history.
How long after a dose change should TSH be rechecked?
No sooner than six weeks. The ATA gives steady state as reached “in 6 weeks (approximately five to six half-lives)”, and a TSH drawn earlier reflects the old dose more than the new one. The label allows re-adjustment every four to six weeks; in pregnancy the TSH is measured every four weeks because requirement is still rising.
What is the TSH target on levothyroxine?
For standard adult replacement the ATA’s therapeutic target is a TSH within the reference range, 0.4–4.0 mIU/L. In pregnancy the aim is between the lower limit and 2.5 mIU/L. Over 70 to 75 years the ETA accepts about 1–5 mIU/L. After differentiated thyroid cancer the 2025 ATA guideline gives no numeric target at all.
Why has my TSH gone up when my dose has not changed?
Most often because absorption has changed. Levothyroxine needs an empty stomach and at least four hours’ separation from calcium, iron and proton pump inhibitors, and coffee taken with the tablet is enough to reduce absorption. A new supplement, a new PPI, a change in when the tablet is taken, pregnancy, or coeliac disease will all raise a TSH without any change in prescription.
Why is there no thyroid cancer option on this calculator?
Because there is no longer a number to put in it. The 2015 ATA guideline gave risk-stratified TSH suppression targets; the 2025 guideline withdrew them, states only that TSH should be kept below or within the reference range, and no longer recommends complete suppression. Suppressive dosing is set by the treating team against the response to therapy.
Related calculators
References
- 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):1670–751 — target TSH 0.4–4.0 mIU/L; steady state in 6 weeks.
- Levothyroxine sodium tablets, prescribing information (revised 4/2019), US Food and Drug Administration — “adjust the dose by 12.5 mcg to 25 mcg increments every 4 to 6 weeks”; elderly or cardiac start 12.5–25 mcg/day increased every 6 to 8 weeks; pregnancy increase 12.5–25 mcg/day with TSH every 4 weeks.
- 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):315–89.
- Pearce SHS, Brabant G, Duntas LH, et al. 2013 ETA Guideline: management of subclinical hypothyroidism. Eur Thyroid J. 2013;2(4):215–28 — recommendations 14, 15 and 22.
- Garber JR, Cobin RH, Gharib H, et al. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Thyroid. 2012;22(12):1200–35.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.