Bethesda Calculator: What Your Category 1-6 Biopsy Result Means + Cancer Risk
You got your thyroid biopsy results back, and somewhere on the pathology report is a number from 1 to 6 (or a Roman numeral from I to VI) under the word “Bethesda.” That single number determines almost everything about what happens next: whether you need more testing, whether you need surgery, and how worried you should be about cancer. This calculator helps you understand your category, gives you your malignancy (cancer) risk percentage from both the 2017 and 2023 versions of the Bethesda System, and walks you through the specific decision your doctor will make next[1][2].
I built it to be the post-biopsy decision tool that I wish all thyroid patients had access to before their first endocrinology appointment.
Here’s how to use it:
Pick your Bethesda category from the dropdown. If you got Bethesda 3 or 4, answer the follow-up question about molecular testing. If you got Bethesda 5 or 6, enter your nodule size. Check any optional modifiers that apply (TI-RADS score from a prior ultrasound, family history, head/neck radiation, age 65+). The calculator will then give you your cancer risk percentage along with information on how to keep your thyroid healthy. It’s that easy.
Note: This calculator is a decision support tool, not a diagnosis. Final treatment decisions belong to your endocrinologist, thyroid surgeon, or oncology team, who will integrate clinical context this tool cannot capture, including your full pathology report, ultrasound findings, comorbidities, and personal preferences. Do not change your treatment plan based on this calculator without your treating physician.
Bethesda Calculator
Enter your thyroid FNA biopsy category below to see your malignancy risk, what your cells look like, and your options for molecular testing (Afirma, ThyroSeq) or surgery.
| Category | Name | Risk (2017) | Risk (2023) | Standard Next Step |
|---|---|---|---|---|
| 1 (I) | Non-diagnostic / Unsatisfactory | 5–10% | 5–10% | Repeat FNA with ultrasound guidance |
| 2 (II) | Benign | 0–3% | 2–7% | Clinical follow-up, surveillance ultrasound |
| 3 (III) | AUS / FLUS | 10–30% | 13–30% | Molecular testing, repeat FNA, or lobectomy |
| 4 (IV) | Follicular Neoplasm / SFN | 25–40% | 23–34% | Molecular testing or diagnostic lobectomy |
| 5 (V) | Suspicious for Malignancy | 50–75% | 60–75% | Surgery (lobectomy or total thyroidectomy) |
| 6 (VI) | Malignant | 94–99% | 97–99% | Surgery (extent depends on cancer subtype and stage) |
Written and medically reviewed by Dr. Westin Childs, D.O. Last reviewed: May 11, 2026.
How to Use This Calculator
Step #1: Find Your Bethesda Category on Your Pathology Report
Open your pathology report from your thyroid FNA biopsy.
Look for the word “Bethesda” near the top of the report, usually in the diagnostic line or impression section.
It will be followed by a Roman numeral (I, II, III, IV, V, or VI) or an Arabic number (1, 2, 3, 4, 5, or 6). Both spellings refer to the same system. If you can’t find a Bethesda number, look for the descriptive name: Non-diagnostic, Benign, AUS/FLUS, Follicular Neoplasm, Suspicious for Malignancy, or Malignant. Those names map directly to categories 1 through 6 in order.
Step #2: Pick Your Category (1-6)
Select your category from the dropdown. The options display both the number and the descriptive name so you can match what you see on your report. Each category carries a different malignancy risk range and a different standard next step. Bethesda 1 and 2 lead to surveillance or repeat biopsy. Bethesda 3 and 4 are the indeterminate categories where molecular testing has the biggest impact. Bethesda 5 and 6 mean surgery, with the major decision being how much thyroid tissue gets removed.
Step #3: Answer the Follow-Up Question
If you picked Bethesda 3 or 4, a follow-up question appears asking whether you’ve had molecular testing yet. The three commercial tests are Afirma (Veracyte), ThyroSeq v3 (CBL Path), and ThyGenX/ThyraMIR (Interpace Biosciences). You can answer “not done yet” (the most common answer for new patients), “benign or negative result,” “suspicious or positive result,” or “equivocal.” Each answer changes the decision tree in the results section. A benign molecular result has roughly 95 percent negative predictive value and supports avoiding surgery in favor of surveillance[5].
If you picked Bethesda 5 or 6, a follow-up question appears asking for your nodule size in centimeters. Nodule size is one of the biggest factors in the lobectomy versus total thyroidectomy decision. The 2015 ATA Adult Thyroid Cancer Guidelines support lobectomy alone for low-risk differentiated thyroid cancers under 4 cm with no aggressive features[6]. Leave this field blank if your nodule size is unknown.
Step #4: Check Optional Modifiers
Four optional checkboxes refine the recommendation. The TI-RADS modifier unlocks the combined risk refinement (combining your ultrasound score with your Bethesda result improves diagnostic accuracy to sensitivity around 97 percent and specificity around 92 percent per the 2023 JAMA Network Open concordance study)[7]. Family history of thyroid cancer (first-degree relative) and head or neck radiation history both raise your baseline risk above the standard Bethesda category estimates and shift the recommendation toward more aggressive management. Age 65 or older may affect the cost-benefit calculus of surgery versus surveillance for slow-growing low-risk cancers.
Step #5: Review Your Results and Bring Them to Your Doctor
The calculator returns a header card with your category, the descriptive name, and your cancer risk percentage from both the 2017 (original Cibas/Ali) and 2023 (NIFTP-adjusted Ali et al.) Bethesda System updates. Below that, a plain-English explanation of what your category means, followed by category-specific decision support. Use the output as a starting point for your endocrinology appointment, not a substitute for it. Print the page or screenshot the results and bring them with you so you can walk through the questions and options with your doctor.
Understanding Your Results
Your Cancer Risk: 2017 vs 2023 NIFTP-Adjusted Ranges
The result panel shows two cancer risk percentages side by side. The 2017 range comes from the original Cibas and Ali update of the Bethesda System[1]. The 2023 range comes from the third edition update by Ali et al., which adjusted the malignancy risk percentages to account for NIFTP reclassification[2]. NIFTP (Noninvasive Follicular Thyroid Neoplasm with Papillary-like nuclear features) was reclassified in 2016 from a malignant tumor to a “borderline” neoplasm with very low recurrence risk[4]. This reclassification reduced the apparent malignancy risk of some indeterminate Bethesda categories.
For practical purposes, the 2023 ranges are slightly more conservative for Bethesda 4 and 5 (because lesions previously called cancer are now reclassified as borderline) and slightly higher for Bethesda 2 (because of better real-world false-negative data). The differences between the two range sets are small but real, and showing both gives you transparency about which version your endocrinologist or pathologist may be referencing.
The Indeterminate Categories (Bethesda 3 and 4)
Bethesda 3 and 4 are called “indeterminate” because the cells don’t give cytopathology enough information to call them benign or malignant. About 30 percent of FNA biopsies fall into one of these two categories[2]. Bethesda 3 (AUS/FLUS) means some atypical cells were seen but not enough to commit to a more specific diagnosis, with malignancy risk 10 to 30 percent. Bethesda 4 (Follicular Neoplasm or Suspicious for Follicular Neoplasm) means the cells look like a follicular tumor, but cytopathology can’t distinguish a benign follicular adenoma from a malignant follicular carcinoma without examining the capsule of the nodule, with malignancy risk 25 to 40 percent.
The historical default for both categories was diagnostic lobectomy (half-thyroidectomy) to get a definitive answer. Modern practice has shifted strongly toward molecular testing first because it avoids unnecessary surgery in 50 to 70 percent of indeterminate cases[5].
Molecular Testing: Afirma, ThyroSeq, ThyGenX
Three major commercial molecular tests are available for indeterminate thyroid nodules. The Afirma Gene Sequencing Classifier (Veracyte) has sensitivity around 91 percent and specificity around 68 percent, making it strongest at ruling out cancer. It returns a binary result of Benign or Suspicious. ThyroSeq v3 (CBL Path) has sensitivity around 94 percent and specificity around 82 percent, and tests 112 genes for mutations and gene expression patterns. It returns Negative, Currently Negative, or Positive with a specific mutation profile. ThyGenX/ThyraMIR (Interpace Biosciences) has sensitivity around 89 percent and specificity around 85 percent, combining mutation analysis with microRNA expression in a two-panel format.
A benign molecular result has roughly 95 percent negative predictive value, which means the residual cancer risk is around 5 percent. That’s low enough that most endocrinologists are comfortable moving to ultrasound surveillance instead of surgery[5]. A suspicious or positive result with specific high-risk mutations (BRAF V600E in particular, which is associated with classical papillary thyroid carcinoma) confirms the need for surgery and may inform the extent of the operation. Most insurance plans cover molecular testing for indeterminate FNA results, but check with your insurance and your endocrinologist’s office before assuming coverage.
Beyond the Biopsy: The Functional Layer
Whatever your Bethesda result, the underlying thyroid environment matters. Most thyroid nodules form in glands that are inflamed, autoimmune, or hormonally suppressed. Even when a nodule turns out to be cancer, the underlying thyroid environment affects how aggressively the cancer behaves and how the rest of your thyroid will function long-term. Patients with elevated TPO antibodies and inadequately treated hypothyroidism have higher rates of nodule formation than patients with quiet antibody status[8].
Optimizing your thyroid antibodies (TPO, thyroglobulin), free T3, free T4, and TSH can change the trajectory of future nodule formation and slow the growth of existing ones. If you want to assess your underlying thyroid health, check your labs against optimal ranges with the Optimal Thyroid Lab Test Calculator, screen for autoimmune thyroiditis with the Hashimoto’s Symptom Quiz, or run your ultrasound features through the TI-RADS Calculator to confirm the imaging suspicion level that led to your biopsy.
Frequently Asked Questions
Bethesda 1 means your biopsy was non-diagnostic or unsatisfactory, which happens when the sample didn’t contain enough thyroid cells to make a diagnosis. About 10 to 15 percent of FNA biopsies come back non-diagnostic on the first attempt due to too much blood, too little tissue, or only cyst fluid being collected[1]. This is not a cancer diagnosis and not a benign diagnosis. The biopsy simply needs to be repeated, typically 4 to 12 weeks later with ultrasound guidance.
Bethesda 2 means your biopsy cells look benign on cytopathology. This is the most common result and the most reassuring. The 2017 risk range was 0 to 3 percent. The 2023 update adjusted this slightly upward to 2 to 7 percent to better reflect real-world false-negative rates[2]. No biopsy or surgery is indicated for Bethesda 2 in most cases. The standard next step is periodic ultrasound surveillance, with interval depending on the original nodule features. The small residual risk comes from sampling error, which is why your endocrinologist may still want imaging follow-up in 12 to 24 months.
Bethesda 3 (AUS or FLUS, depending on the specific report) means your biopsy showed some atypical cells but not enough to commit to either a benign or malignant diagnosis. The malignancy risk is 10 to 30 percent under the 2017 ranges and 13 to 30 percent under the 2023 NIFTP-adjusted ranges[1][2]. Roughly 70 to 90 percent of Bethesda 3 nodules turn out to be benign on further evaluation.
You don’t necessarily need surgery. Modern practice has shifted strongly toward molecular testing as the first next step. Three commercial tests are available (Afirma, ThyroSeq, ThyGenX). A benign molecular result has roughly 95 percent negative predictive value and supports moving to ultrasound surveillance instead of surgery, avoiding unnecessary thyroidectomy in 50 to 70 percent of indeterminate cases[5]. A suspicious molecular result confirms the need for diagnostic lobectomy at minimum. If molecular testing isn’t available or affordable, the alternatives are repeat FNA in 3 to 6 months (which yields a more definitive result in about half of cases) or proceeding directly to diagnostic lobectomy. Ask your endocrinologist explicitly about molecular testing before defaulting to surgery.
Bethesda 4 (Follicular Neoplasm or Suspicious for Follicular Neoplasm, sometimes shortened to FN or SFN) means your biopsy cells look like a follicular tumor. The cancer risk is 25 to 40 percent under the 2017 ranges and 23 to 34 percent under the 2023 NIFTP-adjusted ranges[1][2]. The difference between Bethesda 3 and Bethesda 4 is that Bethesda 3 is mostly about cellular atypia, while Bethesda 4 is specifically about cells that look like they could be a follicular neoplasm.
Cytopathology has a fundamental limitation in this category. The cells of a benign follicular adenoma and a malignant follicular carcinoma look identical under the microscope. The only way to tell them apart is to remove and examine the entire nodule to see whether cancer cells have invaded the capsule. This is why diagnostic lobectomy used to be the default next step. Modern practice now favors molecular testing first (Afirma, ThyroSeq, ThyGenX) for the same reasons it favors testing in Bethesda 3: it can convert a “maybe cancer” result into a more confident answer without surgery. About 60 to 75 percent of Bethesda 4 nodules turn out to be benign follicular adenomas on final pathology. If surgery is needed after molecular testing, lobectomy (half-thyroidectomy) is typically sufficient because the diagnosis can only be confirmed on full pathology of the removed nodule.
Bethesda 5 (Suspicious for Malignancy) means most of the features of thyroid cancer are present on your biopsy cells but not all of them. The cancer risk is 50 to 75 percent under the 2017 ranges and 60 to 75 percent under the 2023 NIFTP-adjusted ranges[1][2]. About 60 to 75 percent of Bethesda 5 nodules turn out to be cancer on final pathology. The remaining 25 to 40 percent turn out to be benign or low-grade lesions like NIFTP.
Yes, surgery is the standard recommendation. The bigger question is whether you need a lobectomy (removing only the affected lobe, half-thyroidectomy) or a total thyroidectomy (removing the entire thyroid). Recent literature notes that nearly half of Bethesda 5 patients may be overtreated with total thyroidectomy when lobectomy would suffice[3]. The 2015 ATA Adult Thyroid Cancer Guidelines support lobectomy alone for nodules under 4 cm, confined to one lobe, with no extra-thyroidal extension, no suspicious lymph nodes, no contralateral nodules, no family history of thyroid cancer, and no prior head or neck radiation[6]. If you meet those criteria, ask your surgeon explicitly whether lobectomy is appropriate before defaulting to total thyroidectomy. Intraoperative frozen section pathology lets the surgical team upgrade to total thyroidectomy mid-operation if cancer is confirmed and the extent of disease warrants it.
Bethesda 6 (Malignant) means your biopsy clearly shows cancer cells. The cancer risk is 94 to 99 percent under the 2017 ranges and 97 to 99 percent under the 2023 ranges[1][2]. So yes, this is a definitive cancer diagnosis. The cytopathology usually also indicates the cancer subtype: most commonly papillary thyroid carcinoma (the most common and most treatable form), followed by medullary thyroid carcinoma, anaplastic thyroid carcinoma, or thyroid lymphoma in rarer cases.
The diagnosis is scary but the prognosis for most thyroid cancers is excellent. The 5-year survival rate for localized differentiated thyroid cancer (papillary and follicular) is near 100 percent[9]. Surgery is the standard treatment. The extent depends on the cancer subtype, tumor size, and risk features. For papillary thyroid cancer under 4 cm with no aggressive features and no contralateral nodules, lobectomy alone may be adequate per 2015 ATA guidelines[6]. For larger tumors, multifocal disease, extra-thyroidal extension, lymph node involvement, family history, or any medullary or anaplastic subtype, total thyroidectomy is preferred. Many patients also need central neck dissection if lymph node involvement is suspected. Post-operative care includes thyroid hormone replacement (sometimes at TSH-suppressing doses) and possible radioactive iodine therapy depending on risk stratification.
Molecular testing is genetic and molecular analysis of the cells from your FNA biopsy. Three major commercial tests are available in the United States. Afirma Gene Sequencing Classifier (Veracyte) has sensitivity around 91 percent and specificity around 68 percent, making it best at ruling out cancer in indeterminate nodules. ThyroSeq v3 (CBL Path) has sensitivity around 94 percent and specificity around 82 percent, and tests 112 genes for mutations and gene expression. ThyGenX/ThyraMIR (Interpace Biosciences) has sensitivity around 89 percent and specificity around 85 percent and combines mutation analysis with microRNA expression. Each test is performed on the same cells already collected during your biopsy, so most patients don’t need a repeat needle stick.
You probably need it if your biopsy came back Bethesda 3 or 4 (the indeterminate categories). Modern practice strongly favors molecular testing first for both of these because it can convert a “maybe cancer” result into a more confident answer without surgery. A benign molecular result has roughly 95 percent negative predictive value and supports moving to surveillance instead of surgery, avoiding unnecessary thyroidectomy in 50 to 70 percent of indeterminate cases[5]. A suspicious molecular result confirms surgery is the right path and may identify specific high-risk mutations (BRAF V600E in particular) that inform the extent of the operation. You probably don’t need it if your biopsy was Bethesda 1, 2, 5, or 6 because the cytology alone gives a confident answer in those cases. Most insurance plans cover molecular testing for indeterminate FNA results. Ask your endocrinologist’s office to verify coverage before defaulting to surgery on a Bethesda 3 or 4 result.
References
- Cibas ES, Ali SZ. The 2017 Bethesda System for Reporting Thyroid Cytopathology. Thyroid. 2017;27(11):1341-1346. https://www.liebertpub.com/doi/10.1089/thy.2017.0500
- Ali SZ, Baloch ZW, Cochand-Priollet B, et al. The 2023 Bethesda System for Reporting Thyroid Cytopathology. Thyroid. 2023;33(9):1039-1044. https://www.liebertpub.com/doi/10.1089/thy.2023.0141
- Lee S, Jang JY, Park HS, et al. Can Cytologic and Sonographic Features Help Prevent Overtreatment of Bethesda V Thyroid Nodules? Journal of Surgical Research. 2021. https://www.sciencedirect.com/science/article/abs/pii/S0022480421003656
- Nikiforov YE, Seethala RR, Tallini G, et al. Nomenclature Revision for Encapsulated Follicular Variant of Papillary Thyroid Carcinoma: A Paradigm Shift to Reduce Overtreatment of Indolent Tumors. JAMA Oncology. 2016;2(8):1023-1029. https://jamanetwork.com/journals/jamaoncology/fullarticle/2513234
- Steward DL, Carty SE, Sippel RS, et al. Performance of a Multigene Genomic Classifier in Thyroid Nodules with Indeterminate Cytology: A Prospective Blinded Multicenter Study. JAMA Oncology. 2019;5(2):204-212. https://jamanetwork.com/journals/jamaoncology/fullarticle/2715388
- Haugen BR, Alexander EK, Bible KC, et al. 2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer. Thyroid. 2016;26(1):1-133. https://www.liebertpub.com/doi/10.1089/thy.2015.0020
- Concordance of the ACR TI-RADS Classification With Bethesda Scoring and Histopathology Risk Stratification of Thyroid Nodules. JAMA Network Open. 2023;6(8):e2331612. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2809293
- Anil C, Akkurt A, Ayturk S, Kut A, Gursoy A. Hashimoto’s thyroiditis is not associated with increased risk of thyroid cancer in patients with thyroid nodules: a single-center prospective study. Thyroid. 2010;20(6):601-606. https://www.liebertpub.com/doi/10.1089/thy.2009.0450
- SEER Cancer Statistics Review (CSR), Thyroid Cancer 5-Year Relative Survival. National Cancer Institute. https://seer.cancer.gov/statfacts/html/thyro.html
- Alexander EK, Kennedy GC, Baloch ZW, et al. Preoperative diagnosis of benign thyroid nodules with indeterminate cytology. New England Journal of Medicine. 2012;367(8):705-715. https://www.nejm.org/doi/full/10.1056/NEJMoa1203208