Cashinator
Tracking and splitting expenses, along with the intelligently calculated cash settlement, is a core feature of the Cashinator app.
The app automatically calculates who owes whom and determines the best way to settle debts. Cashinator optimizes transactions to ensure that, in the end, as few and as simple payments as possible are needed.
Since we've received a lot of feedback from users thinking the debt calculations are incorrect, we'd like to clarify—using this example—how Cashinator arrives at these (actually optimal) results.
Steffi, Mareike, and Tom are on a journey together in Europe. They make a total of three transactions:
Transaction 1:
Steffi pays for the accommodation, which costs 300 €. At this point:
1. Mareike owes Steffi 100 € and
2. Tom owes Steffi 100 €.
Transaction 2:
Since Mareike doesn’t have enough money for the long-awaited skydiving experience, Tom lends her 200 €.
Now, the debts are:
1. Mareike owes Tom 200 €,
2. Mareike still owes Steffi 100 €, and
3. Tom still owes Steffi 100 €.
Transaction 3:
Even after Mareike's skydiving, Steffi is still afraid of flying and decides to take an overpriced train ticket for 200 € back home.
Her debit card doesn't work, so Mareike covers the cost.
If we now sum everything up, we see that at the end of this journey, the following payments need to be made for everyone to be settled:
1. Mareike gives Tom 200 €.
2. Steffi gives Mareike 100 €.
3. Tom gives Steffi 100 €.
After these three payments, everyone would be even again. This is, in fact, the calculation any of us would logically make.
Three transactions might be correct and expected, but isn't there an even simpler way? Yes! Cashinator optimizes all transactions mathematically so that the fewest and simplest possible payments need to be made. Instead of three separate payments, Cashinator suggests just one single transaction:
1. Mareike gives Tom 100 €.
That’s all that needs to happen, and suddenly everyone is settled! Even though Steffi originally paid for the accommodation, everything balances out. Looking at the final balances (especially at the end of the journey), it becomes clear why:
Balance after Transaction 1:
Steffi: +200 €, Mareike: -100 €, Tom: -100 €.
Balance after Transaction 2:
Steffi: +200 €, Mareike: -300 €, Tom: +100 €.
Balance after Transaction 3:
Steffi: 0 €, Mareike: -100 €, Tom: +100 €.
After Transaction 3, Steffi is fully settled—no one owes her money, and she owes no one, even though she initially covered the accommodation.
When Mareike gives Tom 100 €, the final balance for all three participants is exactly 0 €.
With just a single payment, all debts among the participants are settled, and no further transactions are necessary.
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