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This is really a personal preference, depending on many factors, including the length of and likely variability in your journey to the airport, knowledge of the airport, the time of departure, day of week and season. Most crucially, how stressed or relaxed you would like to feel before you fly.
The most variable and uncontrollable factors that will affect you will be parking (if relevant), and the security queue.
45 minutes should be ample, 30 minutes would be cutting it fine but I would recommend planning on arriving an hour before to ensure a stress free departure.