The last halving was in November 2012.
Between September 2011 and September 2012 price (BTC/USD on Bitstamp) changed by +105% (i.e. it doubled).
Between September 2012 and September 2013 price changed by +1040%.
Between September 2013 and September 2014 price changed by +240%.
Between September 2014 and September 2015 price changed by -46%.
On average, price changed annually in that 4-year period by +335%, but that's not the point - the point is that doubling (or even significant price increases) has not been restricted to halving years.
Ok so lets's assume we will make another 50% gain this year the price would be ~$675.
If we could gain 50% every year for the next 4 years this would bring us to a price of $3417,18/BTC. (675 * 1,5^4 = 3417,18)
This won't make OP a millionaire but definitely is a nice amount of money I would say.
Definitely! Past performance is obviously no guarantee for the future, and I can certainly imagine that the annual quadrupling we've seen on average might be reduced significantly, but even "moderate" annual rises would result in fantastic prices in 2020.
(In most any other market talking about 50% annual rises year on year would be ludicrous... we're talking about it as a realistic possibility, one that's not as impressive as the past!)