Whatever you feel comfortable with. To own stocks means to accept upside and downside risk. If you can't afford to lose 40% in a year because you might need the money within 10 years, reexamine your risk profile. It's okay to have cash on hand that you might need for a down payment, wedding, car purchase. If you're talking about money you won't touch in 10+ years and you won't panic sell, then don't try to time the market.