I’ve developed another couple of spreadsheets that are free to use.
The ‘historical mortgage rates’ spreadsheet is a one stop shop for historical mortgage interest rates (since 2005) across a wide range of mortgage terms. The sheet also provides a summary of the average rates for each term over this timeframe too.
As it stands in early 2026, the 1 year mortgage rate has had the lowest average interest rate over the last 21 years. The 4 and 5 year rates the worst (on average). On any given month, the 1 year rate is the lowest rate over 60% of the time.
Just because a mortgage rate is the lowest at a point in time, doesn’t necessarily mean it is the best rate for you moving forward. That is because during the timeframe you fix, other interest rates may become more attractive. That is where the second resource comes in handy. The ‘which mortgage term has been the best calculator’. I know, doesn’t exactly roll off the tongue does it.
This calculator lets you enter your current mortgage details as well as any start date from the last 21 years. From there you can see what mortgage term strategy was best historically speaking. Always refixing every 6 months for example. Or every two years. Or always fixing at the lowest available rate. The results for each strategy are provided including the average interest rate, the total interest paid, and the total remaining loan balance.
In addition, the spreadsheet provides the results for 10,000 forward looking simulations. Also known as a Monte Carlo simulation. The purpose of this is to see the probability of interest rates in the future, based off historical data.
These are two really valuable tools that I hope can help you with some of your mortgage decisions. You can find both spreadsheets on the mortgage calculator page, along with further descriptions around how the spreadsheets were made and what information is included.
If you do find value from the spreadsheets, please do share on social media or even privately. Knowing they are adding value to as many kiwis as possible is the greatest gift for my time.
If you need help with any financial decisions, then get in touch today.
The information contained on this site is the opinion of the individual author(s) based on their personal opinions, observation, research, and years of experience. The information offered by this website is general education only and is not meant to be taken as individualised financial advice, legal advice, tax advice, or any other kind of advice. You can read more of my disclaimer here