Numbers/Excel: How can I calculate this as a percentage?

This isn't as easy as a simple formula....It's going to depend on the interest, the rise in property values (or decline) etc.

Once you have all the figures for the parameters, it's an easy job to work it out, but you need the figures first.

 

<Contributed Amount> / <Original House Price> = X / 100

Say the house was worth £200,000 initially.

£36,150 / £200,000 = X / 100
X = (36,150 / 200,000) * 100 = 18.075% investment

Now, figure the current price and how much they should get back using the same type of formula.

<Return Amount> / <Current House Price> = <percentage invested> / 100

or from the above example, assume the house is worth £300,000 today :

<Return Amount> / £300,000 = 18.075 / 100

<Return Amount> = (18.075 * 300,000) / 100 = £54,225

This only takes in the values you put into it. In your case, your initial house price was the total you put down and your parents put down (£82,500 + £36,150 = £118,650). The current house price is the amount that you'll be getting back AFTER the remaining mortgage is paid off. If say your house is worth £500,000, but you still owe £350,000 mortgage, you'll only be getting £150,000 back and thus that is the price listed as <Current House Price> not the street value.

This assumes that you paid the mortgage the whole time without any help. If they contributed to the monthly mortgage, you'd have to figure out how much of that they invested in.

Let me know if there is anything more you could use help with there. It isn't that hard, unless there are other things that come up. I'd recommend being completely honest with them and showing them all the paperwork; don't want a few dollars hurting family relationships.

 

I guess I should have stated that his original house price should be the total amount put down, not the street price. Thus he should be using the £118,650 for that part of the calculation, which results in the 30.5% you listed.

 

If you're just wanted to give you parents a percentage of the £35k profit based on you initial investment it's pretty straight forward.

Total Invested = £82,500 (You) + £36,150 (Parents) = £118,650

Percentage invested by Parents = (£36,150/£118,650)*100 = 30.46%

30.46% of £35k profit is £10,611