500 meters, its electronically limited, and it can be achieved in any area (except no fly zones). You have to be careful of windspeed, because the wind is much different at 500meters. Get an app called UAVforecast and check the wind levels at higher altitudes.
Also, stay far far far away from the airport, because airplanes can be as low as 500meters on approach as far away from the airport as The Avenues. Be extra careful, don't be stupid, when in doubt check flight radar 24.
Edit * Always use flight radar 24 if you are going above 400meters. Do it EVERY single time. Air traffic routes change often.