Non-invasive age estimation is critically important for many field studies but often it represents a significant challenge. In rodents, upper incisors represent a part of a cranium which can be readily measured in an alive animal. We propose an age estimation method based on the measurements of both upper incisors' width (IW) for a subterranean rodent, Ellobius tancrei. The IW measurements for 77 laboratory-born females and 81 males were fitted, separately for the sexes, by sigmoidal Gompertz growth functions to obtain the asymptotic values. Based on the data set encompassing pre-asymptotic ages, we then derived a polynomial regression model with log-transformed age as a predictor. The analysis revealed no statistically significant sex difference in growth patterns. Derived model explained 91% of IW variation and was used to obtain predicted values of age and their 95% prediction intervals through inverse calculations. We conclude that IW is a potentially useful age indicator for mole voles and possibly other rodents in cases when invasive or time-consuming methods are non-appropriate.