Here's the code I use to do it.
; -- Frames Per Second counter.
; Place into the main program loop where it will be executed each frame. The variables used here do not need to be declared globlly as this will occur automatically if the routine is placed in the main program. The value of 'milli_secs' should be set from the 'MilliSecs()' Blitz function at the start of the main program loop.
FPS_framecounter = FPS_framecounter + 1
If milli_secs >= FPS_timeout Then
FPS_timeout = milli_secs + 1000
FPS_framecount = FPS_framecounter
FPS_framecounter = 0
EndIf
Color 180, 0, 0
Text 350, 5, "FPS"
Color 255, 255, 255
Text 400, 5, FPS_framecount
;^^^^^^
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