Which of the following best represents the formula for estimating the number of teeth in the first two years of life?

• A. Age in months minus 4
• B. Age in months minus 6
• C. Age in months minus 8
• D. Age in months minus 10

Answer: (B)

Estimating how many teeth have erupted in the first two years uses a simple rule of thumb: subtract six from the child’s age in months. Teeth typically begin to erupt around six months, and the count increases as months pass. So, at a given age in months, about that many teeth minus six have erupted. For example, at twelve months you’d expect around six teeth; at eighteen months around twelve; at twenty-four months around eighteen. This is a practical, quick estimate clinicians use when checking developmental progress, even though individual eruption timing can vary.

Other constants would misalign with the typical eruption timeline—subtracting four would overestimate early on, while subtracting eight or ten would undercount as age increases. The six-month mark best fits the common eruption pattern during the first two years.