BSP Staging and Grading Cheat Sheet (2026) + Free Calculator

The BSP staging and grading system is the UK clinical standard for diagnosing periodontitis. It replaces the old "chronic vs aggressive" terminology and gives a much more useful clinical picture. This cheat sheet boils down the BSP implementation of the 2017 World Workshop classification into a one-page reference.

Stage (severity) - based on worst-site interproximal bone loss

Note that Stage IV may also be assigned in cases with significant tooth loss due to periodontitis (≥5 teeth lost) or complex rehabilitation needs - even if bone loss alone would only reach Stage III.

Grade (rate of progression) - based on bone loss / age ratio

Worked example: a 50-year-old patient with 25% bone loss has a ratio of 0.5 - that's Grade B. The same patient at age 30 with 25% bone loss would be 0.83 - Grade B. At age 25 with 25% bone loss, the ratio is 1.0 - still Grade B (just). At age 20 with 25%, the ratio is 1.25 - Grade C.

Smoking and diabetes: in the BSP implementation, these are documented alongside the diagnosis as risk factors rather than directly modifying the Grade calculation. Grade C is reserved for cases where progression is genuinely rapid based on the bone-loss-over-age ratio.

Engagement (before root surface debridement)

Engagement is checked after oral hygiene instruction, risk factor control and supragingival scaling (Step 1 of the BSP UK S3 guideline), before subgingival instrumentation. Two sets of figures are in use, so say which one you follow:

• BSP UK S3 guideline targets (West et al., 2021, as summarised by SDCEP): plaque 20% or less, or at least a 50% reduction from baseline; marginal bleeding 30% or less, or at least a 50% reduction, or targets agreed between patient and clinician.

• Healthy Gums DO Matter (HGDM) thresholds for its partial-mouth scores (HGDM toolkit, 2nd edition, 2019): Modified Bleeding Score under 35% and Modified Plaque Score under 30%, or more than 50% improvement in both. In non-smokers the bleeding score takes precedence; in smokers and oral nicotine users the two count equally. HGDM raised these from 20% and 30% after its diagnostic study, because partial-mouth scores underestimate disease.

• Engaging - Meets the targets your practice uses, or is doing their best within limits such as poor manual dexterity (a clinical judgement). Move on to subgingival instrumentation.

• Not engaging - Re-motivate, re-instruct and repeat the assessment.

Stability (after active therapy)

At the post-therapy review:

• Stable - BoP <10%, PD ≤4mm, no BoP at 4mm sites. Move to maintenance.
• In remission - BoP ≥10% but no BoP at 4mm sites, PD ≤4mm. Increase maintenance frequency.
• Unstable - PD ≥5mm OR PD ≥4mm with BoP. Re-treat.

MPS (Modified Plaque Score) - HGDM toolkit

A partial-mouth plaque score on six index teeth (Ramfjord's teeth): UR6, UL1, UL4, LL6, LR1 and LR4 (16, 21, 24, 36, 41 and 44). On each tooth, score three surfaces: interproximal, buccal, and palatal or lingual.

• 0 - No plaque, even when a probe is skimmed along the gingival margin
• 1 - Plaque seen only with the probe
• 2 - Plaque visible without a probe

Add the scores, divide by 36 and multiply by 100. If an index tooth is missing, use the nearest equivalent (the other central incisor or a lateral incisor, the second premolar, the second molar). If there is none, score it N and divide by 6 less for each N (30 instead of 36).

MBS (Modified Bleeding Score) - HGDM toolkit

The same six teeth, scored differently. Run the probe gently at 45 degrees round the gingival sulcus in a continuous sweep and watch for up to 30 seconds. Score four sites on each tooth (mesial, distal, buccal, and palatal or lingual): 0 for no bleeding, 1 for marginal bleeding. Add the scores, divide by 24 and multiply by 100 (divide by 20 if one tooth is N).

This is bleeding from the gingival margin, a measure of daily plaque control. It is not bleeding on probing from the base of the pocket, which goes on the 6-point pocket chart. SDCEP describes the same two scores. The engagement thresholds for both are in the Engagement section above.

Putting it all together - example diagnoses

Stage III, Grade B, currently unstable, generalised periodontitis. Risk factors: smoker.

Stage IV, Grade C, currently engaged in active therapy, localised periodontitis. Risk factors: poorly controlled type 2 diabetes (HbA1c 9.2%).

Stage II, Grade A, currently stable on maintenance, generalised periodontitis. No active risk factors.

Common pitfalls

1. Forgetting to multiply percentage by 100 in the Grade calculation. If bone loss is 0.30 (30%) and age is 50, the ratio is 30/50 = 0.6 (Grade B), not 0.30/50 = 0.006.
2. Using full attachment loss instead of bone loss for staging. Staging is based on radiographic bone loss at the worst site, not CAL.
3. Forgetting that Stage IV requires either >66% bone loss OR ≥5 teeth lost / complex rehabilitation needs.
4. Confusing engagement with stability. Engagement is checked before subgingival instrumentation; stability is after active treatment.
5. Mixing up the two sets of plaque and bleeding targets. The BSP S3 figures (20% and 30%) and the HGDM thresholds for its six-tooth scores (30% and 35%) are different. Say which you use.

Sources and clinical references

• British Society of Periodontology: implementing the 2017 classification
• British Dental Journal: periodontal diagnosis in the context of the 2017 classification system
• BSP UK S3 clinical practice guidelines for the treatment of periodontitis
• Healthy Gums DO Matter toolkit (BSP)
• SDCEP: monitoring plaque and bleeding

Frequently asked questions

What is the quickest way to grade periodontitis?

Use the worst-site radiographic bone loss percentage divided by patient age. Under 0.5 is Grade A, 0.5 to 1.0 is Grade B, and over 1.0 is Grade C.

Does smoking or diabetes change the BSP diagnosis statement?

In the BSP/HGDM workflow, smoking and diabetes are recorded in the risk factor assessment and diagnosis statement after stage, grade, extent, and current disease status are calculated.

When is periodontitis currently unstable?

Periodontitis is currently unstable when there are pockets of 5mm or more, or pockets of 4mm or more with bleeding on probing.

Calculate stage and grade automatically

Our free BSP Perio Calculator does the maths: enter age, bone loss percentage, teeth lost, extent, complexity, smoking and diabetes, and it returns the diagnosis statement. No sign-up needed.

In AI Notes, the same calculator opens in Clarification Mode when perio details are missing from the consultation. You confirm the values and the diagnosis goes into the draft note in the standard format, ready for you to review.