It seems obvious: outside IR35 means more money in your pocket, so it must mean a bigger mortgage. On take-home, that is true. On borrowing, it is not the whole story — and the gap between the assumption and the reality is where a lot of contractors leave money on the table. At the right lender, an inside-IR35 role can support just as much borrowing as an outside one, and sometimes more. This article works through the comparison that actually decides it.
Principles here are stable; exact lender figures are confirmed at application.
The take-home reality: outside wins
There is no argument here. Outside IR35, your company invoices the full contract value and you manage your own tax, typically keeping far more of the contract than an inside contractor on the same rate, who has tax and National Insurance deducted at source. Pound for pound on the same day rate, outside IR35 leaves you better off. If take-home were what lenders assessed, outside would win every time.
The mortgage reality: it depends on the lender
But the best contractor lenders do not assess take-home — they assess the contract. Inside or outside, a gross-value lender applies the same calculation to the same day rate:
Day rate x 5 days x 46 weeks = assessed annual income
On a £600-a-day contract, that is £138,000 assessed whether you are inside or outside IR35 — because the contract value is the same. At a gross-value lender, the inside and outside contractor on the same rate borrow the same amount. The take-home difference, which feels so decisive, simply does not enter the calculation. This is the point most contractors miss: for borrowing, the lender’s method matters far more than your IR35 status.
The twist: inside can borrow more
Here is where it inverts. Inside-IR35 roles often carry a rate premium, precisely because the take-home is lower and the market compensates for it. A £520 outside role and a £620 inside role can leave you in a similar net position after tax. But for a gross-value lender, that premium is pure upside: the £620 inside rate assesses at £142,600, comfortably above the £119,600 the £520 outside role produces. At the right lender, the inside role with a genuine rate premium borrows more than the outside role it might replace. The tax calculation and the mortgage calculation are different sums, and conflating them costs money in both directions.
Worked comparison
Illustrative only, at a gross-value lender using a 4.5x multiple:
- Outside IR35, £520 a day: £119,600 assessed → around £538,000 borrowing.
- Inside IR35, £620 a day (typical premium): £142,600 assessed → around £642,000 borrowing.
- Inside wins by roughly £100,000 here — despite similar take-home — because the higher rate drives the assessment.
The one thing that decides it
All of which comes back to a single factor: the lender. An inside-IR35 contractor at a net-assessment lender borrows a fraction of what the same contractor borrows at a gross-value lender — a difference that can exceed £200,000 on a mid-range rate. That gap dwarfs the inside-versus-outside question entirely. So the honest answer to “which lets me borrow more?” is: whichever your rate is higher on, provided the application lands with a lender that assesses the gross contract value. Get the lender right and your IR35 status is a detail; get it wrong and it is a catastrophe.
There is one further nuance among gross-value lenders: some assess the contract before employer’s National Insurance is funded from it, some after, a difference of roughly 13.8% of assessable income. Identifying which treatment each lender applies is part of placing an inside-IR35 case well — and part of why specialist advice earns its keep on exactly these cases.