Most capital projects have an implementation lag. We examine the effect of implementation lag on a levered firm’s investment decision. The main finding is that implementation lag can potentially have a substantial effect on a levered company’s investment trigger, and this effect can be significantly different from that of an unlevered company. The exact relationship between lag and investment trigger depends on the level of debt used by the firm. For an optimally-levered firm, a crucial determinant of the lag-investment relationship is the fraction of investment cost that has to be incurred upfront. If this fraction is small, investment trigger is a decreasing function of implementation lag and the effect can be economically significant. If this fraction is large, investment trigger can be either increasing or decreasing in lag, depending on parameter values, but the magnitude of the effect is not large. Optimally levering a firm makes the implementation lag more investment-friendly relative to an unlevered firm, thus it is possible that the lag has a negative effect on investment if the firm is unlevered but a positive effect if the same firm is optimally-levered. For an optimally-levered firm, implementation lag generally has a non-negative effect on investment. 2015 Elsevier B.V. All rights reserved.