Gain-Bandwidth product question

[bitrex]

If I have an op-amp with say, a hypothetical bandwidth of 1 MHz, and I use it in a configuration where I have a gain of 10, I know that I will only have unity gain at an input frequency of 100kHz. What I am wondering is how I go about calculating what the effective cutoff frequency is, i.e. where the gain is down -3dB? Thanks!

[uart]

.. and I use it in a configuration where I have a gain of 10, I know that I will only have unity gain at an input frequency of 100kHz. ...

No that's incorrect. So long as the other poles (apart from the dominant pole that sets the 1MHz GBWP) are above 100kHz then 100Khz will indeed be a very good approximation to the actual -3dB frequency.