How this tool works
The calculator applies the 2017 World Workshop framework (Tonetti, Greenwell and Kornman, 2018) in four steps. Every step shows up in the reasoning trail, so you can check which finding set each part of the diagnosis.
- Case definition. Staging only starts if the patient is a periodontitis case: interdental CAL at 2 or more non-adjacent teeth, or buccal/oral CAL of 3 mm or more with pockets over 3 mm at 2 or more teeth. The CAL must not be explained by traumatic recession, cervical caries, a third molar affecting the distal of the second molar, an endodontic lesion draining through the margin, or a vertical root fracture.
- Stage. The initial stage comes from interdental CAL at the worst site. Radiographic bone loss (RBL) is used only when CAL isn't available. Then tooth loss from periodontitis and each complexity factor are checked. The final stage is the highest stage any of them points to. Nothing can lower it.
- Extent. Localized means under 30% of teeth involved; 30% or more is generalized. A molar/incisor pattern is named instead when it fits.
- Grade. Start from the best evidence of past progression: direct evidence (older radiographs or CAL records) first, then % bone loss ÷ age at the worst tooth, then the case phenotype. With no evidence, the rules say to assume Grade B. Smoking and diabetes then only raise the grade.
Staging criteria at a glance
| Finding | Stage I | Stage II | Stage III | Stage IV |
|---|---|---|---|---|
| Interdental CAL, worst site | 1–2 mm | 3–4 mm | 5 mm or more | 5 mm or more |
| Radiographic bone loss | Under 15% (coronal third) | 15–33% (coronal third) | Middle third or beyond | Middle third or beyond |
| Teeth lost to periodontitis | None | None | 1–4 | 5 or more |
| Maximum probing depth | Up to 4 mm | Up to 5 mm | 6 mm or more | 6 mm or more |
| Other complexity | Mostly horizontal bone loss | Mostly horizontal bone loss | Vertical defect of 3 mm or more; class II/III furcation; moderate ridge defect | Needs complex rehabilitation for masticatory dysfunction, secondary occlusal trauma (mobility 2+), severe ridge defect, bite collapse, drifting, flaring, or fewer than 20 teeth (10 opposing pairs) |
The calculator reads the probing-depth row the same way as the others: 5 mm fits Stage II, so it can move a Stage I case up.
Grading criteria at a glance
| Evidence | Grade A | Grade B | Grade C |
|---|---|---|---|
| Bone or CAL loss over 5 years | None | Less than 2 mm | 2 mm or more |
| % bone loss ÷ age | Under 0.25 | 0.25 to 1.0 | Over 1.0 |
| Case phenotype | Heavy biofilm, little destruction | Destruction matches biofilm | Destruction beyond what biofilm explains; rapid or early-onset patterns |
| Smoking (modifier) | Non-smoker | Under 10 cigarettes/day | 10 or more a day |
| Diabetes (modifier) | No diabetes | HbA1c under 7.0% | HbA1c 7.0% or higher |
For example, 40% bone loss at age 50 gives 40 ÷ 50 = 0.8, which is Grade B. If that patient smokes 12 cigarettes a day, the grade rises to C.
When CAL and bone loss disagree
The AAP chart and Tonetti 2018 both say to use CAL first. The calculator follows that rule and warns you when RBL points higher. Some teaching flowcharts, including the one used in a 2021 Irish Dental Association case series, stage from bone loss instead. If your program teaches that, choose "The higher of CAL and RBL" under Rule options. The trail always shows what each measure pointed to.
Published examples the calculator reproduces
We test the logic against worked cases, including these:
- Tonetti 2018: a 4 mm CAL with a class II furcation (short root trunk) moves Stage II to Stage III. Posterior bite collapse makes it Stage IV.
- Tonetti 2018: Stage II, assumed Grade B, with poorly controlled type 2 diabetes becomes Grade C.
- JIDA 2021, Part 2, case 1: 54-year-old non-smoker, CAL up to 6 mm, about 50% bone loss, generalized. 50 ÷ 54 = 0.93, so the result is generalized periodontitis, Stage III, Grade B.
- JIDA 2021, Part 2, case 2: 34-year-old smoking 15 a day, CAL up to 7 mm, a class II furcation, 40% bone loss. 40 ÷ 34 = 1.18, so the result is generalized periodontitis, Stage III, Grade C.
Limits
- The classification is a guide. The authors stress that it should be applied with sound clinical judgment, and so does this tool.
- For extent, the AAP chart only says "teeth involved". Enter your count of teeth with periodontal breakdown, as a share of the teeth present.
- Tonetti's original grading table also has a grey row on systemic inflammation (flagged as needing more evidence) and a biomarker row with no set thresholds. Neither is in the AAP chart, so both are left out.
- Use the Gingival Index and Plaque Index calculators to record inflammation and plaque alongside the diagnosis.
Frequently asked questions
Should I stage from CAL or from radiographic bone loss?
The 2017 rule sets the initial stage from interdental CAL at the site of greatest loss, and uses radiographic bone loss only when CAL isn't available. If the two disagree, the calculator keeps CAL and flags the mismatch. Some teaching flowcharts stage from bone loss; switch to "the higher of CAL and RBL" under Rule options if you follow one.
Can a single complexity factor change the stage?
Yes. Tonetti and colleagues note that one complexity factor is usually enough to shift the diagnosis up. For example, a class II furcation moves a Stage II case to Stage III. Complexity factors never move a stage down.
How do smoking and diabetes change the grade?
They can only raise it. Fewer than 10 cigarettes a day, or diabetes with HbA1c under 7.0%, points to at least Grade B. Ten or more a day, or HbA1c of 7.0% or higher, points to Grade C. A non-smoker without diabetes keeps the grade set by the evidence.
What if I don't have older radiographs?
Then the grade comes from indirect evidence: the percentage of bone loss at the worst tooth divided by the patient's age. Below 0.25 is Grade A, 0.25 to 1.0 is Grade B, and above 1.0 is Grade C. With no evidence at all, the rules say to assume Grade B.
Does the stage go down after successful treatment?
No. If treatment removes a complexity factor, the stage stays where it was, because that history still matters during maintenance. The exception is successful regeneration that improves CAL and bone support of the tooth. Use "Stage assigned before treatment" when you re-stage.
Sources
- Tonetti MS, Greenwell H, Kornman KS. Journal of Clinical Periodontology 45(Suppl 20):S149-S161 (also J Periodontol 89(Suppl 1):S159-S172, doi:10.1002/JPER.18-0006). Staging and grading of periodontitis: Framework and proposal of a new classification and case definition. 2018. Accessed October 26, 2026.
- Papapanou PN, Sanz M, Buduneli N, et al. Journal of Periodontology 89(Suppl 1):S173-S182. Periodontitis: Consensus report of workgroup 2 of the 2017 World Workshop on the Classification of Periodontal and Peri-Implant Diseases and Conditions. 2018. Accessed October 26, 2026.
- American Academy of Periodontology. Staging and Grading Periodontitis (chart). 2018. Accessed October 26, 2026.
- American Academy of Periodontology. Three Steps to Staging and Grading a Patient. 2018. Accessed October 26, 2026.
- Nolan M, Aljudaibi S, Harrison P, Winning L. Journal of the Irish Dental Association 67(1):30-32. Application of the new periodontal classification: Part 2. 2021. Accessed October 26, 2026.
- da Mata C, Hayes M, Roberts A. Journal of the Irish Dental Association 67(2):88-91. Application of the new periodontal classification: part 3. 2021. Accessed October 26, 2026.
Last reviewed by the Dental Health Time editorial team, against the sources above. How we review.