The multiplier, or the change in equilibrium GDP that will occur per any change in spending, can be determined by calculating the fraction of any change in income that survives all of the leakages and goes on to start the next round of spending. That is, the multiplier depends upon the fraction of any change in income that becomes...
the change in exports
the change in savings
the change in imports
the change in domestic consumer spending
the change in disposable income
the change in business investment spending