Vocabulary input frequency influences age of acquisition, and is also an essential control for investigating the influence of other factors. We propose a new method of frequency estimation, self-report. 918 Danish-speaking parents of 12-36-month-old children estimated their frequency of use of 725 words. Self-report was substantially correlated with both language sample based frequencies (0.67) and frequencies of a large written corpus of Danish (0.58). Correlations within vocabulary categories between frequency and age of acquisition, restricted to words occurring in the language samples, were comparable for the two estimates. Overall, self-report based frequency estimates appear to have a promising degree of validity, which reflects their greatest strength, independence of the situation.