There is a great amount of evidence showing that adults solve single-digit multiplications and additions automatically. Nevertheless, evidence regarding subtraction and division is scarce. The present study explores whether the solving of single-digit subtractions is automatic or not. Seventeen psychology students took part in our experiment. They have to judge the correctness of single-digit additions. In the “false additions” the result could be the subtraction of the operands (e.g., 7+3=4) or could be unrelated with the operands (e.g., 7+3=2). The data analysis showed the presence of an interference effect, this is, worse performance in the subtraction condition than in the unrelated condition. These results suggest that subtraction solving is highly automatic.