According to the Sraffian Supermultiplier model, originally presented in Serrano (1995) and further discussed in Freitas and Serrano (2015), output growth is shaped by the evolution of the autonomous components of demand: export, autonomous consumption, government expenditure and autonomous business expenditure. As a demand-led growth model, the Sraffian Supermultiplier displays several desirable properties: a) the extension to the long-run of the Keynesian Hypothesis (Garegnani, 1992); b) an investment function based on the accelerator mechanism, without at the same time engendering Harrodian instability; c) the absence of any necessary relation between the rate of accumulation and normal income distribution; d) an equilibrium level for the degree of capacity utilization equal to the normal, cost-minimizing one. More recently, Allain (2015) and Lavoie (2016) provided similar models, in the form of amended versions of the Neo-Kaleckian model. In this paper, at first, we make an explicit distinction among different kind of public expenditures and we focus on different types of fiscal policies: generic ones (e.g. on bridges and roads) and “mission oriented” that set a new direction for the economy (e.g. the ICT direction in the US during the 80s and 90s, or the German Energiewende direction in the 2000s) and that has led to major technological advances, such as the DARPA (Department of Defense) investment on ARPANET which became in the modern-day internet, the ARPA-E (Department of Energy) investments in renewable energy, or the National Institutes of Health investments in the biotechnology sector (Block and Keller, 2011; Mazzucato, 2013). This type of investment does not increase the stock of capital, but promote the transformation and modernization of existing capital goods. We also assume that firms’ R&D are, at least partially, positively affected by public expenditure oriented to promote innovation. In other words, specific types of public spending, for example military expenditure, are able to induce and stimulate R&D of private firms (Mazzucato, 2013, 2016, 2017; Deleidi and Mazzucato, 2018) by generating spin-offs through which research and innovation are developed and diffused to other sectors (Pivetti, 1992). In these cases, public investment creates a new landscape (rather than simply fixing market failures), which influences the expectations of business, resulting in an increase in private expenditure. We then implant the Supermultiplier mechanism in a simplified but complete and stock-flow consistent structural macroeconomic model inspired by the pioneering work of Godley and Lavoie (2016). Five sectors are considered: working-class households (i.e. the recipients of labour incomes and a share of interest payments on bank deposits), capitalist households or rentiers (i.e. the recipients of the remaining interest payments on bank deposits, entrepreneurial profits and other financial incomes), production firms (or non-financial corporations), banks (including commercial banks, financial intermediaries and the central bank), the government sector and the foreign sector. After having introduced the sectoral balance sheet and the transactions-flow matrix used to define the macroeconomic identities which assure the accounting coherence of the model, we slightly modify the baseline consumption functions, given that autonomous consumption is taken as a simple function of households’ net wealth. The rationale is that net wealth is crucial in determining households’ creditworthiness and is influenced by the structure of interest rates. In addition, coefficients defining propensities to consume out of wealth may well be assumed to mirror banks’ willingness to lend. So, this hypothesis allows keeping things as simple as possible, while capturing the impact of interest rates on household consumption plans. The latter are also affected by the social status of households, as wage-earners are assumed to be characterised by a higher propensity to consume (out of both income and wealth) than capitalists or rentiers. Portfolio decisions of capitalists have been modelled in line with Tobinesque principles. Net export has been considered using a constant growth rate for export, while defining import as a linear function of output. A standard equilibrium condition has been also added to clear the stock market though price adjustments. We also assume that the Central Bank is willing to act as a lender of last resort for the government sector instead. In other words, the Central Bank buys the (residual) amount of government bonds which are left unsubscribed by private investors at a given price. Expectations matter and a simple adaptive behaviour is assumed. Model’s reactions to shocks have been tested though numerical simulations. Unknown coefficients have been given theoretical but ‘realistic’ values, based on available data and the literature. The main results of the numerical simulations are the following: unsurprisingly, government mission-oriented innovation spending is the policy entailing the highest multiplying effect on output, followed by routine spending. Tax reduction has also a positive impact on output and its components, mainly through an increase in consumption levels. However, the effect is far below that of an increase in government spending, due to household saving ‘leakages’. In fact, tax reduction is (slightly) more effective when benefits wage-earners, because they are assumed to have a lower propensity to save of out income compared with the rentiers. The impact of a loose fiscal policy on government deficit and the stock of debt is usually one of the main concerns for the policy makers. We show the effect on deficit, using two different baseline scenarios: a theoretical zero-deficit zero-debt situation; and a more realistic case where both deficit and debt ratios are turned positive. While the deficit to GDP ratio always increases following an expansionary fiscal policy, the effect is just temporary. Once again, government mission-oriented innovation spending turns out to be the best option, as it is characterised by the smallest peak in the deficit to GDP ratio following the shock. The ratio then falls sharply and stabilises below the baseline level (that is, the difference with the baseline value remains negative). Routine spending is the second-best option, while tax reductions have a stronger impact on deficit and can take more time to be reabsorbed (especially tax cuts on rentiers’ income). The same goes for the stock of debt to GDP ratio. An increase in mission-oriented innovation spending of the government also entails a lower debt peak compared to other options and then allows reducing permanently the debt to GDP ratio. Notice that other expansionary fiscal policies also enable cutting the debt to GDP ratio in the long run, but at a much slower pace. The point is that government spending, particularly mission-oriented innovation spending, triggers an innovation cascade in the private sector, thereby increasing steadily the growth rate of output. Other expansionary policies have also a positive impact on output, but their effects should be expected to be less dramatic. Following a positive shock on mission-oriented innovation spending, all output components growth rates converge towards their new equilibrium value. While the change in firms’ innovation pace can be short-lived, the impact on other output components turns out to be long-lasting. The adjustment of growth rates following exogenous shocks to other autonomous growth rates has also been tested. The numerical simulations broadly confirm the main insights of the Supermultiplier model and allow to avoid some simplifications usually necessary in the related theoretical literature on autonomous demand-led growth.