Stacking (cumul, in French-language programs) is the practice of funding one project from several non-dilutive sources at once. It is how deep tech companies assemble real leverage: a federal tax credit, a national or regional grant, an agency contribution and an equity round can all support the same work. But programs are designed to avoid double-funding the same dollar, so they interact through 2 main mechanisms that a founder must understand before assuming the money simply adds up.
The first is base reduction. Government assistance received from one program usually reduces the eligible expenditure base of another claimed on the same costs. The classic case is Canadian: an IRAP contribution lowers the SR&ED-qualified expenditures, so the tax credit earned on those costs falls. The programs are complementary but not additive, and the combined take is always less than the arithmetic sum of each taken alone. The second is the aggregate cap. Many grant and contribution programs limit total public funding to a percentage of eligible project cost (a maximum aid intensity), so beyond a ceiling, adding another public source crowds out the others rather than increasing the total.
The operator discipline is to model the stack as a joint optimization, not a sum. That means allocating costs across programs to maximize the combined result, sequencing applications so one does not silently erode another, and respecting each program’s cumul rules and aid-intensity caps. Done well, stacking turns a thin equity round into a fully-funded milestone; done naively, a founder budgets for $550,000 of support, receives $480,000, and discovers the gap exactly when the runway is tightest.