How far back should I backtest?

I am testing a new strategy and it is manual, and very time consuming, Im just wondering whyat the general vibe is out there, as for how far back I should back test my strategy to be happy its consistent. Its an intraday strategy Im trading 5min charts if thats relevant.

thanks guys!

a thousand trades schould give you a first indication, if a strat might be viable or not, and even that is on the low end. Preferably you should have +10.000 trades to be quite sure that the strategy is viable in the long-term.

Most systems work like a charm for a hundred or more trades until they go back to negative. But there are only a handful that work in the long-term.