The following figure, is the consumption curve. The ${45}^{\circ }$ line is the aggregate supply curve. At point A, consumption = income i.e., $\left(\mathit{Y}=\mathit{C}\right)$ represents the autonomous consumption i.e., consumption at zero level of income. Steps for derivation of supply curve from consumption curve is as follows :

(i) Corresponding to in the consumption function we have-in the saving function. That is, there are negative savings equal to autonomous consumption at $\mathit{Y}=0$. This is represented by $\mathrm{S}$ on the negative axis in the lower panel.

(ii) At point $\mathrm{A}\left(\mathrm{Y}=\mathrm{C}\right)$. This implies that all the income is spent on consumption expenditure.
Thus savings equal to zero. This is shown as $\mathit{S}$ $=0$ in lower panel. This point is also known as the Break-even point.

(iii) Beyond the break-even point, by connecting points $\mathit{S}$ and $\mathit{B}$ we derive the straight upward sloping saving curve.

(iv) $\mathrm{SS}$ is the required saving curve.