Quick answer: IBS-C and IBS-D are subtypes of irritable bowel syndrome sorted by stool form, not by how you feel. Under the Rome IV criteria, you look only at days with an abnormal bowel movement. IBS-C means more than 25% of those stools are hard (Bristol types 1–2) and fewer than 25% loose (types 6–7). IBS-D is the reverse. IBS-M means both are above 25%. A clinician confirms the subtype, ideally from a 2-week stool diary.
"Am I IBS-C or IBS-D?" sounds like it should have an easy answer. In practice many people aren't sure, because their gut swings between the two, or because they've only ever described their bowels from memory.
The good news is that the rule your doctor uses is simple and public, and the evidence it needs is something you can collect. This guide explains IBS-C vs IBS-D vs IBS-M, shows the counting rule on a worked 14-day log, and explains why your subtype can change.
Key takeaways
- IBS subtypes are defined by stool form on the Bristol Stool Form Scale, counted only on days with abnormal bowel movements [1][2].
- The cut-off is 25%: hard stools (types 1–2) for IBS-C, loose stools (types 6–7) for IBS-D, both for IBS-M. If no pattern fits, it's IBS-U (unclassified) [1].
- The ACG guideline recommends daily diaries for 2 weeks, ideally while off medicines that change bowel habits, for the most accurate subtype [1].
- More than half of people with IBS change subtype over a year, so your subtype isn't fixed [1].
What's the difference between IBS-C and IBS-D?
IBS-C (IBS with constipation) and IBS-D (IBS with diarrhea) share the same core: recurring belly pain linked to bowel movements and changes in stool frequency or form [2][3]. What separates them is which kind of abnormal stool dominates.
| Subtype | On days with abnormal stools… | What people often notice |
|---|---|---|
| IBS-C | More than 25% are Bristol type 1–2 (hard, lumpy) and fewer than 25% are type 6–7 [1] | Straining, infrequent stools, feeling of not emptying, bloating between bowel movements |
| IBS-D | More than 25% are type 6–7 (mushy, watery) and fewer than 25% are type 1–2 [1] | Urgency, loose stools, pain often eased or triggered around bowel movements |
| IBS-M (mixed) | More than 25% are type 1–2 and more than 25% are type 6–7 [1] | Swinging between constipation and diarrhea, sometimes within the same week |
| IBS-U (unclassified) | Meets IBS criteria but fits none of the above [1] | Abnormal stool days are too few or too mixed to label |
NIDDK puts it in plain words: for IBS-C, more than a quarter of your stools are hard or lumpy and less than a quarter are loose or watery, and the reverse for IBS-D [4]. The ACG guideline notes that people with IBS-D tend to report pain and urgency with each bowel movement, while those with IBS-C report more symptoms between bowel movements [1].
Which Bristol stool type is IBS?
No single Bristol type is "IBS". People with IBS often have plenty of normal days with type 3–5 stools. What matters for subtyping is the share of type 1–2 and type 6–7 stools on the abnormal days. Types 1–2 count as constipation-type stools and types 6–7 as diarrhea-type stools [1]. Types 3, 4 and 5 don't count toward either side.
How is your IBS subtype worked out?
Your subtype is worked out from a stool record, not a single description. The ACG guideline's recommended method is [1]:
- Use the Bristol Stool Form Scale to record each bowel movement's form.
- Count only days with an abnormal bowel movement. A day counts if it has at least one type 1–2 or type 6–7 stool. Rome IV introduced this rule because people with IBS have many normal days, and counting them watered down the result [8].
- Record medicines and any changes. Tell your clinician which medicines can affect bowel habit. Do not stop, start or adjust them to complete a diary; the clinician can interpret the record in that context.
- Ask what recording period is useful. A two-week diary is one clinical format, not a requirement to postpone care.
- Apply the 25% thresholds to the bowel movements on those abnormal days.
This only sorts the pattern. Whether you have IBS at all is a clinical diagnosis that also covers pain, timing and ruling out other conditions [5]. Our guide to how IBS is diagnosed walks through that part.
Worked example: a 14-day Bristol stool log
Here's how the counting works on a two-week log. The data is illustrative, made up to show the method. It's not from a real person.
| Day | Bowel movements (Bristol type) | Abnormal day? |
|---|---|---|
| 1 | 4 | No |
| 2 | 2 | Yes |
| 3 | none | No |
| 4 | 1, 2 | Yes |
| 5 | 4 | No |
| 6 | 6, 6, 7 | Yes |
| 7 | 3 | No |
| 8 | 2 | Yes |
| 9 | 4 | No |
| 10 | 5 | No |
| 11 | 2 | Yes |
| 12 | none | No |
| 13 | 6 | Yes |
| 14 | 4, 1 | Yes |
Step 1: list the bowel movements on abnormal days. Days 2, 4, 6, 8, 11, 13 and 14 hold 11 bowel movements: 2 · 1, 2 · 6, 6, 7 · 2 · 2 · 6 · 4, 1.
Step 2: count each side.
- Types 1–2: 6 of 11 = 55%
- Types 6–7: 4 of 11 = 36%
Step 3: apply the thresholds. Both are above 25%, so this log fits an IBS-M pattern.
Here's the twist. If you counted every bowel movement across all 14 days (16 in total), hard stools would be 6 of 16 (37.5%) and loose stools exactly 4 of 16 (25%). That's not more than 25%, so the same person might look like IBS-C. The counting method changes the answer, which is why a written log beats a memory, and why the final call belongs to your clinician.
A few practical tips while you log:
- Log every bowel movement, not just the bad ones. Missing normal days makes the abnormal ones look more common.
- Log no-go days too. Days with no bowel movement are useful context for constipation.
- Note medicines, illness and travel. A course of antibiotics or a stomach bug can skew two weeks.
Tracking your stool pattern in Get Regular
For ongoing records, explore the Get Regular food and symptom tracker. Check the current workflow, privacy information and access before entering sensitive information. A recorded association is a question to investigate, not a confirmed trigger.
Can IBS-C change to IBS-D?
Yes. Changing subtype is common. The ACG guideline notes that more than half of people with IBS change their predominant subtype over a one-year period, and recommends checking the subtype routinely rather than assuming it's fixed [1]. Many people on IBS forums describe going from mostly constipation to mostly diarrhea, or settling into a mixed pattern.
If your pattern shifts, a fresh two-week log is worth more than your old label. A sudden or lasting shift, especially with any red flag below, is a reason to see your doctor rather than relabel yourself. If you're dealing with swings between the two, our guide to constipation then diarrhea covers other causes too.
Why your IBS subtype matters
Your subtype matters because many IBS treatments are designed for one subtype. According to the ACG guideline, most IBS medicines were developed with one specific subtype in mind, and a treatment chosen for the wrong subtype could make symptoms worse [1]. NIDDK makes the same point: some medicines work only for some types of IBS or make other types worse [5].
It also shapes testing. For example, the ACG guideline recommends a blood test for celiac disease, and suggests stool and blood markers of inflammation, in people with suspected IBS and diarrhea symptoms [1].
A note on definitions: in 2026 the Rome Foundation released updated Rome V criteria, which change some thresholds for diagnosing IBS itself [6]. The 2-week diary method above follows Rome IV and the 2021 ACG guideline. Ask your clinician whether the newer criteria change anything for you.
When to see a doctor
See a doctor before labeling yourself with any subtype if your bowel habits have changed recently or you've never been assessed. Get prompt care for [3][5][7]:
- blood in your stool, or black, tarry stool
- unexplained weight loss or signs of anemia
- diarrhea that wakes you at night
- fever or vomiting with bowel symptoms
- severe pain that doesn't ease after a bowel movement
- symptoms starting after 50, or a family history of colon cancer, inflammatory bowel disease or celiac disease
FAQ
Which is more common, IBS-C or IBS-D?
Estimates vary between studies and depend on which criteria and counting rules are used. The more useful question is which pattern your log shows over two weeks, since that's what guides treatment.
Can you have IBS and normal poop?
Yes. Many people with IBS have plenty of normal type 3–5 stools. That's exactly why Rome IV counts only days with abnormal stools when deciding your subtype [1][2].
What counts as diarrhea in IBS?
For subtyping, diarrhea-type stools are Bristol types 6 (mushy, ragged pieces) and 7 (entirely liquid) [1]. Frequency alone doesn't make a stool "diarrhea" if its form is normal.
Does IBS-M mean my IBS is worse?
Not necessarily. IBS-M describes the pattern, not the severity. Severity depends on how much pain, urgency and disruption you have, which is worth tracking separately with a 0–10 rating.
Sources
- Lacy BE, Pimentel M, Brenner DM, et al. ACG Clinical Guideline: Management of Irritable Bowel Syndrome. Am J Gastroenterol. 2021;116(1):17–44. https://pubmed.ncbi.nlm.nih.gov/33315591/
- Mearin F, Lacy BE, Chang L, et al. Bowel Disorders. Gastroenterology. 2016 (Rome IV). https://pubmed.ncbi.nlm.nih.gov/27144627/
- Rome Foundation. Rome IV Criteria. https://theromefoundation.org/rome-iv/rome-iv-criteria/
- NIDDK. Definition & Facts for Irritable Bowel Syndrome. https://www.niddk.nih.gov/health-information/digestive-diseases/irritable-bowel-syndrome/definition-facts
- NIDDK. Diagnosis of Irritable Bowel Syndrome. https://www.niddk.nih.gov/health-information/digestive-diseases/irritable-bowel-syndrome/diagnosis
- Goyal MK, Goyal O, Sehgal T, et al. What is new in Rome V? Redefining diagnostic criteria and clinical pathways in disorders of gut-brain interaction. Indian J Gastroenterol. 2026. https://pubmed.ncbi.nlm.nih.gov/42753081/
- Cleveland Clinic. Irritable Bowel Syndrome (IBS). https://my.clevelandclinic.org/health/diseases/4342-irritable-bowel-syndrome-ibs
- Schmulson MJ, Drossman DA. What Is New in Rome IV. J Neurogastroenterol Motil. 2017. https://www.jnmjournal.org/journal/view.html?doi=10.5056%2Fjnm16214
This article is for general education and isn't medical advice. Get Regular is a tracking app. It doesn't diagnose or treat any condition. If you have red-flag symptoms or ongoing changes in your digestion, talk to a doctor.