Investment models typically explain only a small share of the total investment variation within or between firms. A reason for this may be that those models do not explicitly differentiate between the decision to invest and the decision about the level of investment. In this paper, a two-steps theoretical framework and estimation procedure are developed to take into account the different nature of both decisions. ‘Nearly zero’ investments are considered to be small replacement or maintenance investments and treated as ‘zero’ investments. The applied two-step Heckman model shows that the decision to invest is significantly related to available capital (-), wealth (+), debts (-), output prices (+), land price growth (+), capital price growth (-), energy price growth (+), revenues (+) and age of the firm owner (-). The level of investment is also related to available capital, wealth, debts, output price, capital price growth and age of the firm owner, but with opposite signs for debts and capital price growth. Moreover, firm size positively affects the level of investment (but not the decision to invest). The fact that both decisions are affected differently proves the rationale of using a two-step investment model but further research is needed to increase the explanatory power of the models.