Homes in NN12 sell for a median of £361,500 across 663 sales over two years (HM Land Registry), which is +22% against the West Northamptonshire median of £295,446. Set against the local average rent of £1,078 a month (ONS), that implies a 3.6% gross yield here versus 4.4% for West Northamptonshire as a whole.
Rents are published per district, not per postcode, so the yield above applies the West Northamptonshire average rent to NN12 prices. It's the right way to compare postcodes on entry price, but rents do vary street by street, and gross yield ignores costs, voids and mortgage interest.
NN12 averages tell you where to look, not whether one particular flat stacks up. Paste a listing and gemhome runs the actual numbers: yield, cash flow, the lender stress test, EPC work and what the public records say about that specific address.
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