Categorize your TSH level per American Thyroid Association reference ranges. Includes pregnancy-specific ranges and age adjustments.
This calculator categorizes your TSH level per American Thyroid Association reference ranges. Normal TSH is generally 0.4-4.0 mIU/L per ATA. Pregnancy has different ranges. TSH varies by time of day, medications, and health status — a single result is not a diagnosis. Discuss with your healthcare provider.
Written by Ash K · Last updated: June 2026 · Sources cited below
Your TSH (thyroid-stimulating hormone) level is the primary screening test for thyroid function. This calculator interprets your TSH alongside T4 and T3 values to assess whether your thyroid is functioning normally, overactive (hyperthyroid), or underactive (hypothyroid).
Enter your lab values. The calculator compares them against ATA (American Thyroid Association) reference ranges and flags patterns that may warrant further evaluation.
Key Takeaway: TSH is an inverse indicator — high TSH means your thyroid is underactive (hypothyroid), low TSH means it's overactive (hyperthyroid). Normal TSH range is 0.4–4.0 mIU/L for most adults per ATA guidelines. But "normal" has nuance — optimal TSH may be narrower (0.5–2.5 mIU/L) and pregnancy has different thresholds.
| TSH Level | Interpretation | Next steps |
|---|---|---|
| Below 0.1 mIU/L | Likely hyperthyroid | Urgent evaluation — check Free T4, T3 |
| 0.1–0.4 mIU/L | Borderline low | Check Free T4; may be subclinical hyperthyroid |
| 0.4–4.0 mIU/L | Normal range | Routine follow-up |
| 4.0–10.0 mIU/L | Borderline high | Subclinical hypothyroid — check Free T4, antibodies |
| Above 10.0 mIU/L | Likely hypothyroid | Treatment typically recommended |
Note: TSH is counterintuitive — the number goes UP when your thyroid goes DOWN. This is because your pituitary gland produces more TSH to try to stimulate a sluggish thyroid. High TSH = thyroid not making enough hormone. Low TSH = thyroid making too much.
| Hypothyroid (underactive) | Hyperthyroid (overactive) |
|---|---|
| Fatigue, sluggishness | Anxiety, restlessness |
| Weight gain despite normal eating | Weight loss despite normal eating |
| Cold intolerance | Heat intolerance |
| Constipation | Diarrhea |
| Dry skin, brittle hair | Sweating, warm skin |
| Brain fog, poor memory | Racing thoughts, difficulty concentrating |
| Depression | Irritability |
Warning: This calculator interprets lab values against published reference ranges. It does not diagnose thyroid disease. TSH levels must be interpreted alongside clinical symptoms, medical history, pregnancy status, medication use, and sometimes additional tests (Free T4, Free T3, thyroid antibodies, imaging). Always discuss abnormal results with your endocrinologist or primary care provider.
TSH Reference Ranges — per American Thyroid Association
Pregnancy requires different TSH targets. The ATA recommends trimester-specific ranges:
| Trimester | TSH Target |
|---|---|
| First trimester | 0.1–2.5 mIU/L |
| Second trimester | 0.2–3.0 mIU/L |
| Third trimester | 0.3–3.5 mIU/L |
Untreated hypothyroidism during pregnancy increases risk of miscarriage, preterm delivery, and impaired fetal neurodevelopment. If you're pregnant and your TSH exceeds trimester-specific targets, treatment with levothyroxine is typically recommended.
For general pregnancy health tools, see our pregnancy weight gain calculator and due date calculator.
Bottom Line: TSH is the primary thyroid screening test. Normal range: 0.4–4.0 mIU/L. High TSH = underactive thyroid. Low TSH = overactive thyroid. Pregnancy uses tighter ranges. Always interpret with your provider — lab values alone don't diagnose thyroid disease.
What is a normal TSH level?
The standard reference range is 0.4–4.0 mIU/L per ATA guidelines. Some endocrinologists consider 0.5–2.5 mIU/L the "optimal" range, particularly for those trying to conceive.
What does a high TSH mean?
High TSH indicates your thyroid is underperforming (hypothyroid). Your pituitary is producing extra TSH to stimulate a sluggish thyroid. TSH 4.0–10.0 = subclinical hypothyroid. Above 10.0 = overt hypothyroid typically requiring treatment.
What does a low TSH mean?
Low TSH indicates your thyroid is overperforming (hyperthyroid). Your pituitary reduces TSH because the thyroid is already producing excess hormone. TSH below 0.1 warrants urgent evaluation.
Can thyroid problems cause weight gain?
Hypothyroidism can cause modest weight gain (typically 5–15 lbs from fluid retention and slowed metabolism). Significant weight gain is rarely caused by thyroid dysfunction alone — if you've gained 30+ lbs, other factors are likely contributing.
This tool is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your healthcare provider with questions about your health.