BMW i8 depreciation over the next 18 months

[justguess]

Ello ello

Was just after some opinions on the amount of depreciation I can expect for the following car over an 18 month period:

BMW i8
2014
Mileage at start of period: 36,000
Mileage per year: approx 7,000 miles
Purchase price: £57,000

Any sort of response would be greatly appreciated, really just after some ballpark figures.

Cheers

[Mr Whippy]

20% per annum
50% per three years

That seems to still hold true from a trade buy/trade in approach over such timescales.