The questions and original answers

For a first rental property in New Zealand, I’d compare lenders rather than automatically putting the investment mortgage with your existing home-loan bank. Keeping everything together is usually simpler, but splitting the loans can sometimes save you money, give you more flexibility, or reduce your dependence on one bank.

The key is to compare the whole lending arrangement, not just the advertised mortgage rate.

The pros and cons

Option 1: Keep both loans with your current bank

Simpler to manage

• One banking relationship, with repayments and accounts easier to oversee.
• Your existing bank already knows your financial position, which may make the application process more straightforward.
• You may be able to negotiate a better overall deal by bringing more lending to the same bank.
• The downside: you might miss out on a better rate or lending structure elsewhere, and you have less choice if your bank's policies don't suit your plans.

Option 2: Use a different lender for the rental

• You can shop around for a sharper interest rate, cashback offer, or more suitable investment-property lending criteria.
• You diversify your banking relationship rather than relying entirely on one lender.
• You may have more negotiating leverage with your current bank.
• The downside: more paperwork, potentially separate fees and conditions, and possibly more complicated security arrangements if either lender wants a claim over the same property or properties.

The biggest thing to watch: cross-collateralisation

This can matter more than which bank offers the lowest rate.

If your current bank lends against both your home and your rental, it may link the properties as security for the combined lending. This is commonly called cross-collateralisation.

For example:

• You own your home and have built up equity in it.
• You use some of that equity to help buy the rental.
• The bank takes security over both properties for the lending.

That may be convenient initially, but if you later want to sell the rental, refinance one loan, or buy another property, the bank may need to approve the release or rearrangement of its security.

What I'd generally aim for: have the loans clearly separated by purpose, with the security arrangements understood and documented. Ask whether each property can stand as separate security, rather than assuming that separate loan accounts mean separate security.

Using two banks does not automatically solve everything, particularly if the new lender also requires security over your home. Get your lawyer and mortgage adviser to check the proposed arrangements before you commit. ANZ's investment-property borrowing guide also explains that using equity in an existing property doesn't necessarily mean you must take the new loan with the same bank. Borrowing for an investment property

What about tax?

For a typical New Zealand residential rental, the bank you choose does not determine whether your interest is tax-deductible. The use of the borrowed money and the applicable tax rules matter.

From 1 April 2025, interest on funds borrowed for residential rental property can generally be deducted in full, provided the usual tax requirements are met. However, residential rental deductions are generally ring-fenced, meaning excess deductions cannot normally be used against your salary or wages. Keep clear records of what each borrowing was used for, especially if you release equity from your own home to fund the investment. See Inland Revenue's guidance on interest deductions and ring-fencing. Residential property interest limitation rulesResidential rental property deductions

How I'd compare the two options

Ask your current bank and an independent mortgage adviser to compare the same scenario across lenders.

What to compare	Why it matters
Interest rate	Compare the actual rates available for your loan size and equity position.
Cash contribution or cashback	An attractive offer can be offset by fees or repayment conditions.
Loan structure	Check fixed versus floating portions, repayment flexibility and any offset or revolving-credit options.
Lending criteria	Banks can differ in how they assess rental income, existing debt and available equity.
Security arrangements	Understand exactly which property secures each loan and what happens if you sell or refinance.
Future borrowing	Consider whether you might want a second rental or other major borrowing in the next few years.

Don't move your existing home loan simply to get a rental mortgage elsewhere without checking any early repayment costs, fixed-rate break fees or cashback clawbacks.

My rule of thumb

• Choose the same bank if its overall deal is competitive, the structure is flexible enough, and convenience is valuable to you.
• Consider another bank if it offers a meaningfully better overall deal, more suitable lending criteria, or a structure that better supports your longer-term plans.
• In either case, avoid choosing purely on the headline rate. Security arrangements and future flexibility can be worth more than a small rate saving.

A couple of questions that would help me tailor this

Are you planning to use equity in your existing home for the rental deposit, or will you be using cash savings? And is your current home loan fixed or floating?

Those two details can make a real difference to whether keeping the loans together or splitting them is likely to work better for you.