Estimating Net Worth - Real Estate

I have quite a lot of real estate assets - they actually make up a larger percentage of my portfolio than I'd really like (due my wife and I starting out buying a rental property while living with my parents, then later on buying our own place). As they form such a large part of my investment portfolio, I like to be able to update the relevant asset and liability values each month, so that my net worth figure is a reasonable estimate.

The land valuations available via the council rates notices or annual state government land tax calculation are not really much use, as they are based on land value only, and are also only updated on a multi-year cycle.

My method for getting a reasonable monthly figure is to use the bank mortgage statement for the outstanding loan balance at the end of each month, and a simple algorithm for estimating the current valuation of each property. The algorithm is based on the MEAN value of sales in the relevant postcode area (obtained each month from the "suburb snapshot" available by postcode area on the homepriceguide.com.au website for example,2086). I use a simple multiple of the mean price, based on the ratio that applied when I initially purchased the property. For example, my rental property cost 0.9156 x the mean price for the area, so each month I estimate the current valuation as 0.9156 x the latest mean price value.

This allows me to update both house prices and loan balances, and track my progress against what I expected for my property portfolio - paying off the loans over 20 years and property values increasing by approx. 6% per annum in the long run:
It is interesting to also track the percentage change in prices each month, as this clearly shows the "boom & bust" of the Sydney property cycle - as it applies to the specific areas where my properties are.