We present a calculation of single-charge tunneling in a semiconductor quantum dot based on a full self-consistent tight-binding calculation of the charging energies, applicable to quantum dots of realistic size (up to 8 nm diameter). Comparison with recent tunneling spectroscopy experiments on InAs nanocrystals shows excellent agreement and allows an unambiguous assignation of the conductance peaks. For bias voltages V larger that the band gap of the quantum dot we show that both electrons and holes can tunnel into the quantum dot, leading to specific features in the I(V) curves.