One discount on the whole order: divide it by the product amounts
By Erik Nilsen · Kroni3 min read
When an adult and a child each buy a product within one order, a single discount may cover both. You then need a rule for your child's share. Dividing the discount in proportion to the product amounts is one possible family agreement; calculate it before paying.
Find your child's share of the subtotal
In a hypothetical example, your child's optional item costs 60 units and the adult's item costs 90. A discount of 30 units covers both products together. There is no delivery charge, and all amounts are arbitrary teaching numbers.
The product subtotal before discount is 60 + 90 = 150 units. Your child's share is 60 / 150 = 0.40, or 40 per cent. The adult's share is 60 per cent. Under proportional allocation, your child receives 30 × 0.40 = 12 units of discount. They therefore pay 60 − 12 = 48.
The adult receives 30 × 0.60 = 18 units of discount and pays 90 − 18 = 72. Check that 48 + 72 = 120, the same as 150 − 30. The full discount has been divided once, and no units are missing.
Write the rule as well as the answer
You could write: “A discount on the shared product subtotal is divided according to each person's price before discount.” Your child can then understand why their discount is 12 rather than 15. Equal reductions of 15 each are also possible if agreed, but represent a different rule. The child would then pay 45 and the adult 75.
A realistic snag is that the adult earned the voucher on an earlier personal purchase and wants to keep the entire benefit. Clarify that before your child agrees to the order. This calculation does not establish who owns the voucher or which division is morally correct.
Also check which products the discount covers. If only the adult's product qualifies, 150 is the wrong base for treating it as a shared discount. If you divide delivery costs, record those separately under their own agreed rule.
The agreed child share of 48 is what might be deducted from your child's money record here. Do not deduct 60 and add an unlabelled gift of 12 beside it.
Ask your family: “Which rule did we choose, and do both payments add up to the final amount?”
Carry the calculation into your family agreement
Kroni can keep track of your child's virtual balance. The app does not transfer money, so any actual purchase is paid for outside it. Agree on what you will record, then check the amount with your child afterwards. Do not deduct a possible cost as though the purchase had already happened. Read about allowance in Kroni.
