Calculate the effective discount and margin impact of a Buy X Get Y free promotion before you run it.
Enter how many units the customer must buy (X), how many they get free (Y), the unit price and, optionally, unit cost. The set size is X+Y units; the customer pays for X units while receiving X+Y worth of goods. The effective discount is the free units' value divided by the total set value (Y x price / ((X+Y) x price)), and margin impact compares your cost of all X+Y units against the revenue from only X units.
On a Buy 2 Get 1 offer at ₹500 per unit, the customer pays ₹1,000 for 3 units worth ₹1,500, so they save ₹500, an effective discount of 33.3%. If each unit costs you ₹300, your cost for 3 units is ₹900 against ₹1,000 revenue, leaving just ₹100 margin on the whole set.
Yes, on price it works out to a 33.3% effective discount (1 free out of 3), but it moves 3 units instead of 1, which helps clear stock faster than a straight 33% off a single item.
Make sure revenue from the paid units still covers the cost of all units given away. If your margin is thin, use a higher X (e.g. Buy 3 Get 1) so the free unit is a smaller share of the set.
Under GST, 'free' items given with a paid item are generally treated as part of a composite/mixed supply and GST is charged on the amount actually collected; input tax credit on the free goods is usually allowed. Confirm treatment with your CA for your specific case.
Use it to clear slow-moving or overstocked SKUs and to raise units per order, since customers take home more pieces; a flat discount is simpler when you just want a lower headline price.
Commmerce has a built-in offer engine with Buy X Get Y, stacking rules, and GST handling.
See Billing & Checkout
