@I love to travel I'm an acoustical consultant and regularly do such projects.
I'd look at the BNE website as they may have a noise calculator. Or perhaps download a copy of the Masterplan and the Noise chapter may have some maps showing "maximum" type noise curves (N60, N70 etc). Ignore the ANEF curves as they are not going to be of use to you here (interesting though!).
If not, you can get hold of a copy of AS2021, and use google earth to help establish a noise level at your property. It depends on the aircraft type (you'll need to know what flies at night) and your property location relative to the runways. The differences in elevation comes into it too.
All of this will give you a number (ie noise level) outside your house. As a rule of thumb, take 20dB off that number for open windows (or, say, 10dB or 15dB if you live in a house with large or many windows). If that number is more than 50dB, then theoretically your house doesn't meet the standard recommended in AS2021 for bedrooms. Don't worry though AS2021 is a planning tool to provide constructions required to meet the standard.
If you're worried about the noise indoors at night, sleep with the windows closed, in which case the inside level would be about 30dB lower than the outside level.
For reference and generally speaking (we're all different after all), 50 dBA inside a bedroom at night, occurring a few times a night for a short time (eg a flyover) would not be expected to disrupt sleep. Google up a "noise thermometer" which may help you get a feel for equivalent sound levels from other sources. One's tolerance for noise is affected by the character, duration, frequency and expectation of the noise. For eg, a relatively low level noise can be really annoying if you're not expecting it (I'm looking at you Mr Unwrap your lollies in the cinema!).