The following figure, is the consumption curve. The 45∘ line is the aggregate supply curve. At point A, consumption = income i.e., (Y=C) 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 Y=0. This is represented by S on the negative axis in the lower panel.

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

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

(iv) SS is the required saving curve.