Cost per use: calculate a few uses before assuming many
By Erik Nilsen · Kroni3 min read
Cost per use can help your child consider an optional item meant to last. The calculation becomes misleading if you assume lots of future uses simply to make the price look small. Start with a cautious scenario and also show what happens if the item is used more.
Use two scenarios rather than one prediction
In an invented example, your child compares two personal writing notebooks. A simple notebook costs 40 units and a sturdy one costs 120 units. Your child expects eight writing sessions before the simple book is full. The sturdy version has more paper, but nobody knows how long the interest will last. These arbitrary prices are teaching numbers, not assessments of actual products.
The simple book costs 40 / 8 = 5 units per writing session. If the sturdy book is used only eight times, its cost per session is 120 / 8 = 15 units. If it is used 24 times, that becomes 120 / 24 = 5 units. At 24 sessions, it matches the simple book in this calculation.
Write both scenarios for the sturdy book on your paper. “Eight times” and “24 times” are possibilities, rather than a promise your child must fulfil. The purchase price of 120 does not change when you divide it by more uses.
Look for signs that the use is realistic
Consider what your child has already done. Is a previous notebook actually full, or are several almost empty? That is information about this purchase, rather than a judgement of your child. You could wait and finish an existing book before choosing.
A realistic snag is an adult saying: “Then you must use it 24 times.” That turns a comparison into an obligation. Instead, let your child decide whether the uncertainty is worth the larger payment. If another possible use matters, investigate that use specifically before buying.
Quality can matter beyond the number of sessions: paper suitable for particular pens, for example, or a binding that opens flat. Write those features as separate reasons. They do not need to be squeezed into a calculation pretending everything has the same measurable value.
Ask your family: “If you only use it eight times, would it still be worth 120 units to you?” The answer shows whether the decision survives a cautious scenario.
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.
