Calculate attachment loss or signed attachment level from probing depth and gingival margin, solve the inverse measurements, or check all three. The limited stage and indirect-grade reference is educational and requires clinician-confirmed periodontitis and a full dental evaluation.

Educational arithmetic only. Measurements and interpretation require a dentist. CEJ is the cementoenamel junction.

Signed mode: positive coronal to the CEJ, negative for recession. Other modes use a nonnegative amount.

Dental disclaimer: Educational use only. This tool does not diagnose periodontal disease and cannot replace an exam by a licensed dentist/periodontist. Periodontitis staging requires a full clinical evaluation (often including radiographs, tooth loss history, probing depths, and other complexity factors). If you have bleeding gums, pain, swelling, or loose teeth, seek dental care.

Clinical Attachment Loss Formula

The following example problem outlines the steps and information needed to calculate the Clinical Attachment Loss.

CAL = PD - GM

References:
Standardizing clinical evaluations of periodontal condition to guide assessments and diagnoses using the Periodontal Assessment Protocol (GF-PAPro) (2025)
AAP/EFP staging and grading chart (2018). CAL bands are 1–2, 3–4 and ≥5 mm; this calculator leaves fractional gaps unclassified. CAL takes precedence over optional bone-loss percentage. Other complexity findings, disease extent, direct progression, smoking and diabetes can change clinical staging or grading. ADA attachment-loss documentation explains adding recession or subtracting a coronal margin.

Variables:

  • CAL is the clinical attachment loss / level (mm), measured from the CEJ to the base of the sulcus/pocket
  • PD is the probing depth (mm), measured from the gingival margin to the base of the sulcus/pocket 
  • GM is the gingival margin level (mm) relative to the CEJ: GM is positive when the gingival margin is coronal to the CEJ (enlargement), GM is negative when the margin is apical to the CEJ (recession), and 0 when at the CEJ

To calculate the signed attachment level, subtract GM from PD. Because recession is entered as a negative GM value, recession increases the level (for example, PD − (−3) = PD + 3). The calculator reports zero arithmetic loss when the raw signed level is coronal to the CEJ. That reported zero does not determine a unique signed level for inverse calculations. The selected 3 mm coronal margin is an example assumption, not a universal normal value.

How to Calculate Clinical Attachment Loss?

The following steps outline how to calculate the Clinical Attachment Loss.

  1. First, determine the probing depth (PD). 
  2. Next, determine the gingival margin level (GM) relative to the CEJ (use a negative value for recession and a positive value if the margin is coronal to the CEJ). 
  3. Next, gather the formula from above = CAL = PD - GM.
  4. Finally, calculate the Clinical Attachment Loss.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

probing depth (mm) = 9

gingival margin level (mm) = -3 (meaning 3 mm of recession; the margin is 3 mm apical to the CEJ)

CAL = PD - GM = 9 - (-3) = 12 mm