Well I’m surprised the problem you’re posting here is maths and not non-paying friend! So that’s a good start.
It would help if you posted the details:
- how much was her original debt transfer
- was your card balance zero at the time
- have you only ever added the £2000
- how much has she paid you so far
- when did the interest free period end
- what is the new % APR
- what is the promotional APR at the time of your £2000 going on
The deal with her, was that her debt went onto interest free, right?
So her debt is easy to calculate.
Example: If she transferred £5K and has paid you £100 a month for 2 years, then she owes £2600 (24 months x £100 = £2400).
All the interest is on your £2K. So you’ve clocked up interest for 2 years 😳
If that was the agreement, the two separate numbers don’t matter. As of today, she owes her debt minus her payments, you owe the rest. It’s not her fault you used the fact her payments covered the minimum repayment without you actually paying off any of your own debt.
Now you have 2 different interest rates. It’s just maths, you can keep working it out. But it sounds like you will be confused, and she may argue about paying a higher rate than you.
The best option now is she gets her own card and takes her debt back. If there’s a good reason she can’t, then you should get a second card and move your current debt onto that.