Really need some impartial advice on money row with sister!

[Cornberry]

I am in desperate need of an impartial opinion on a sensitive issue.

My parents gave my sister and I a substantial deposit to buy a flat a few years ago. Since that time I have lived in the flat and my sister has lived elsewhere in rented accommodation and now she lives abroad - she had the option to live in the flat too but chose not to. In that time I have taken care of the flat and obviously I (and later on my husband) have paid all the bills and the mortgage etc. We agreed at the outset that my sister and I should split the proceeds 50-50 when it came time to sell.

Now that is time to sell and looking at the figures I realise that our mortgage has come down £30,000 which obviously I have paid since I have been living here. And when we split the money left over after repaying it my sister will get half which seems fair enough because that is what we agreed. However I realise that to bring down our mortgage by £30,000 I have paid in over 50,000 because of the interest. So now it occurs to me that if we split everything 50-50 my sister will get back 15 K, which is half of the money repaid on the mortgage but I will also get in 15 K having paid in 50. This strikes me as unfair. She hasn’t paid anything at all into the flat, which was the agreement and that’s fine, but it seems to me that she should receive a proportion of the increase in value on the property but I am unsure why after I have paid over 50 K into the mortgage to bring it down 30k that she should get 15,000 of it having paid nothing and I should get in 15,000 of it having paid in 50,000. Does that make sense?

Interestingly, my parents do not agree. One of them thinks my sister should get half as agreed and the other one thinks that the point about the interest is a relevant one. I would dearly like to have some opinions from people who are unbiased because I honestly don’t think it’s possible for any of us to be completely impartial on this. I suggested to my sister that she should indeed receive her half of the increase in value but not the repayments, bearing in mind she has never put a cent, and if we split it with her we will she will get more out of the money we paid in than we will.

One issue seems to be one of “changing the goalposts” and my sister has accused me of going back on our agreement to get more money. But the problem is that I was very clueless going into this and I am certain that we had known the considerations at the outset we would have made a different agreement.

Am I being unreasonable?

IABURQO OP also said that she has made overpayments which have brought cost down.

If overpayments haven’t been made then 50/50 is the only way forward. If she has, then I’d be considering getting that back before splitting. Otherwise OP is just giving her sister her money.

Also op would not have been able to buy anything without the sisters deposit

Only if she overpaid on the capital amount (but I'm not sure the OP understands what 'capital' is).

OP you haven’t said how it would have shaken out in terms of the numbers if you had each paid 50% of the mortgage and costs and you had paid your sister half the market rent on the flat? Would the net position be very different? Because as many have pointed out that would have been the reasonable alternative.

The overpayments are unfortunate.

It’s also hard to judge without knowing the dynamics who was doing who a favour by her not living there.

She did at one point she said by the time everything had been paid for her sister would be left with hardly anything a month so even by her own account it balances at 50/50

Some of the posts are astounding.
Saying the sister shouldn't get money because OP paid council tax and water rates, just like almost every single household in Britain? The same bills OPs sister probably had to pay in her own rented accommodation.
Or you should charge her a rental agent fee as because you are living there you are effectively your own landlord. Just so mad.
It doesn't matter what has transpired now, or what's got you thinking you should be more quids in then your sister.
But the agreement was made, you both agreed to it, that is what should happen. You could lose a sister over this.
And your poor mom and dad who did a good thing and have now been dragged into this childish squabble. No good deed goes unpunished.

Take all that away, and I still think your sister should her 50%. I wasn't sure when I started reading but alot of PPs arguments are valid regarding your sister missing out on a rental income and you having a property below market value.
Also, if you Mom and Dad hadn't offered the deposit, and your sister hadn't signed up on the mortgage with you, you wouldn't own a property now and would be renting and throwing all your money away like the rest of us.
You should both be glad your getting a return from your parents generosity.

I don't understand why you would overpay unless you hoped your sister would never claim her 50%
Nobody should have lived in it. You should have rented it out