You can start by looking for 3 other properties that are in the vicinity of the unit you are planning to buy. Try to find the ones with the same or very similar floor plan configuration for a more accurate calculation
- Find the GRM of each respective units by getting the Sales Price from local websites such as property guru, SRX or 99.co
- Estimate the annual rent you can expect to receive for the Unit you are planning to buy
- Multiply the estimated rent with the average of the 3 calculated GRMs of the nearby properties to estimate and see if the unit is planning to sell is undervalued, overvalued or at least fairly valued. Another option is to estimate the GRM for the unit you are looking to buy at a higher or lower level due to the fact that its freehold instead of leasehold, or nearer or further to the amenities etc.
Reference
Stessa’s Definition of Gross Rent Multiplier