Beginner's Guide to Principal and Interest vs Interest-Only

Choosing between principal and interest repayments or interest-only on your home loan affects how much you pay each month and how quickly you build equity in your property.

How Principal and Interest Repayments Work

With a principal and interest loan, each repayment reduces both the amount you borrowed and the interest charged on that balance. Your total debt decreases with every payment, which means the interest portion of each repayment shrinks over time while more goes toward the principal. This structure is sometimes called a table loan because repayments follow a set schedule that clears the debt by the end of the loan term.

Consider a buyer in Auckland who borrows to purchase an owner-occupied property. They take a 30-year principal and interest home loan at a fixed rate for three years. During that fixed period, their fortnightly repayments stay consistent, but the split between interest and principal shifts gradually. In the first year, most of the repayment covers interest. By year three, a larger portion reduces the loan balance. Once the fixed period ends, they can refinance to another fixed term or switch to a floating rate, but the structure remains the same: every payment builds equity.

How Interest-Only Repayments Work

An interest-only loan requires you to pay only the interest charged each period, leaving the principal unchanged. Your loan balance stays the same throughout the interest-only term, which typically lasts one to five years. After that period ends, the loan reverts to principal and interest repayments unless you negotiate another interest-only term with your lender.

This structure is common for investment loans because it keeps repayments lower during the period when rental income may not cover the full cost of a principal and interest loan. It also allows investors to claim the full interest payment as a tax deduction without reducing the deductible debt. For owner-occupied properties, interest-only periods are less common but can be useful during short-term financial constraints, such as parental leave or a business transition.

When Principal and Interest Makes Sense

Principal and interest repayments suit buyers who want to own their property outright within a set timeframe. Each payment reduces what you owe, which means you pay less interest over the life of the loan compared to staying interest-only for an extended period. This structure also builds equity faster, which improves your LVR and can help you avoid or exit a Low Equity Premium if you're borrowing above 80% LVR.

For first-home buyers in Auckland using a low deposit home loan, moving to principal and interest repayments as soon as possible reduces the total interest paid and accelerates the path to 80% LVR. Once you reach that threshold, you can refinance to remove the LEP and access more competitive rates. Lenders like ANZ, ASB, BNZ, Westpac, and Kiwibank all offer principal and interest structures as the default option for owner-occupied lending.

When Interest-Only Makes Sense

Interest-only repayments work when cash flow matters more than equity growth in the short term. Investors often use this structure to maximise tax deductions and free up cash for other purchases or renovations. The lower repayment amount can also improve your borrowing capacity on paper, allowing you to service a larger loan or hold multiple properties.

In a scenario where an Auckland-based investor purchases a rental property using a 70% LVR loan, they opt for a two-year interest-only period on a fixed rate. The rental income covers the interest repayments with a small buffer, and the investor uses the cash flow difference to save for a deposit on a second property. After two years, they switch to principal and interest repayments on the first loan while securing a new interest-only loan for the second purchase. The strategy works because the investor has a clear plan to transition back to principal repayments and uses the interest-only period for a specific purpose rather than deferring equity growth indefinitely.

Switching Between Repayment Structures

You can move between interest-only and principal and interest during the life of your loan, but the timing depends on your lender's policies and your loan terms. Most banks allow you to request an interest-only period at the start of the loan or when you refinance. Switching from interest-only back to principal and interest usually happens automatically at the end of the agreed term, though you can also request it earlier.

If you're on a fixed rate, you may need to wait until the fixed term ends before changing your repayment structure without incurring break costs. On a floating rate mortgage, you can typically adjust your repayment type at any time by contacting your lender. Some loans also include features like redraw facilities or offset accounts that let you reduce the principal faster while keeping the option to access those funds if needed.

How Repayment Structure Affects Borrowing Capacity

Lenders assess your borrowing capacity based on your ability to service a principal and interest loan, even if you apply for interest-only. This means the bank calculates your maximum borrowing amount using the higher repayment figure, regardless of the structure you choose. The difference is that interest-only gives you lower actual repayments once the loan is approved, but it doesn't increase how much you can borrow.

If you're trying to stretch your borrowing capacity for an investment property, the interest-only option won't change the approval amount, but it does improve your cash flow after settlement. That extra monthly buffer can help you meet other financial commitments or save faster for your next purchase. For owner-occupied buyers, the difference in borrowing capacity between the two structures is usually negligible because serviceability is calculated the same way.

Combining Both Structures With a Split Loan

A split loan divides your borrowing between two or more portions, each with its own rate and repayment structure. You might fix part of the loan at a one-year or two-year fixed rate with principal and interest repayments, while keeping another portion on a floating rate with interest-only repayments. This gives you the stability of fixed repayments on part of the loan and the flexibility to make extra repayments or lump sum payments on the floating portion without penalty.

For Auckland buyers juggling multiple priorities, a split structure can balance equity growth with cash flow flexibility. The fixed portion provides certainty around repayment amounts, while the floating portion with interest-only or redraw features lets you respond to changes in income or expenses. Setting up a split loan costs the same as a standard loan, and most lenders offer this option across their product range.

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