How much of my portfolio should be in each asset class?

Your timeline matters most
If you won't need money for 20+ years, a higher stock allocation (70–90%) can handle short-term volatility. If you need funds within 5 years, hold more bonds and cash (40–60%). Most people fall somewhere in between.
Age-based rules
One simple starting point: hold your age in bonds and the rest in stocks. At 30, that's 30% bonds and 70% stocks. At 60, it's 60% bonds and 40% stocks. This isn't perfect for everyone but prevents extremes and adjusts as you age.
Rebalance periodically
Once you've chosen an allocation, don't ignore it. If stocks outperform and now make up 80% instead of your intended 70%, sell some stocks and buy bonds to rebalance. Rebalancing forces discipline: you're selling strength and buying weakness over time.