Who can apply, and how many of you
Most lenders will take two applicants. A smaller number will consider three or four, though even then they will often only use two incomes in the affordability calculation, so a third name adds liability without adding much borrowing power.
You do not have to be related or in a relationship. Friends buying together is more common than it was, and so is a parent going on the mortgage to make the numbers work. What matters to the lender is that everybody named can afford it and everybody named is liable for all of it.
That last point is the one people underestimate. Liability is joint and several, which means each of you is responsible for the whole debt, not your share of it. If one person stops paying, the lender asks the other for the full amount.
How lenders read two credit files
Every applicant is credit checked and the lender looks at all of them. There is no averaging and no balancing out: one person's default or run of missed payments can rule out a lender no matter how clean the other file is.
This is the single most useful thing to establish early. If one of you has had trouble in the past, it changes which lenders will consider you, not whether it is possible at all. Finding that out before you apply avoids a decline sitting on your file while you work it out.
Once the mortgage is live you are financially linked. Any future credit application by either of you can show the other, and that connection outlasts the relationship unless it is formally broken.
The ownership choice most people skip
Separately from the mortgage, you have to decide how you own the property. Your solicitor records it at the Land Registry and it has consequences that last far longer than your current fixed rate.
Joint tenants means you own the whole thing together, in equal shares, with no divided portion. If one of you dies, the other automatically inherits the whole property, regardless of what a will says. It is the usual choice for married couples and long-term partners.
Tenants in common means you each own a defined share, and those shares can be unequal. Your share passes under your will rather than automatically to the other owner. It is the usual choice for friends, for relatives, and for any situation where one person is putting in a much larger deposit.
If you go tenants in common with unequal shares, a solicitor can also draw up a declaration of trust recording who put in what and how the proceeds are divided on a sale. It is not a mortgage document and we do not prepare it, but it is the thing people most regret not having.
What happens if it goes wrong
The mortgage does not care about the relationship. Both of you remain liable for the full amount until it is repaid or one of you is formally removed.
Removing somebody is not paperwork. It is a new application, and the person staying has to qualify for the entire loan on their own income. Plenty of people discover at that point that they cannot, which is worth knowing at the start rather than in the middle of a separation.
It is also why protection matters more on a joint mortgage than a sole one. If one income disappears, the debt does not shrink to match.
What we would do
Look at both of you properly before approaching anybody: incomes, commitments and both credit files. Then pick a lender whose criteria actually fit the pair of you rather than the one with the best headline rate.
And ask you the ownership question early, so you go to your solicitor having already thought about it rather than being asked to decide on the day.
Joint mortgages, answered
How many people can be on a joint mortgage?
Most lenders will take two. A smaller number consider three or four, though usually only two incomes are used in the affordability calculation. All named borrowers are equally liable for the whole debt.
Whose credit score matters on a joint mortgage?
Everybody's. Each applicant is credit checked and there is no averaging: one person's default or missed payments can rule out a lender no matter how clean the other file is. Once the mortgage is live you are financially linked, so future applications by either of you will show the other.
Do we both have to be on the deeds?
Most lenders require anyone on the mortgage to also be an owner. The reverse is not true: somebody can own a share without being on the mortgage, though the lender will usually want them to sign a waiver.
What happens to a joint mortgage if we split up?
Both of you stay liable for the full amount until it is repaid or one of you is removed, and removing somebody means the remaining borrower has to qualify for the whole loan alone.
Can I get a joint mortgage with a friend?
Yes. Tenants in common with a declaration of trust is usually the sensible structure, so each of you owns what you actually put in.
Can one of us be a first-time buyer and the other not?
You can borrow, but you will normally lose first-time buyer stamp duty relief, because the relief requires that none of the buyers has owned a property before. That is a tax question for your solicitor.