(MONEY Magazine) – Mergers and takeovers are in fashion again. Within the past six months, Viacom snapped up Paramount for $10 billion, Northrop bought Grumman for $2.1 billion, Gerber agreed to be acquired by Sandoz for $3.7 billion and Roche Holding agreed to pay $5.3 billion for Syntex.

Each of those deals meant gains of as much as 100% for shareholders of the acquired company. But to maximize profits in a takeover without excessive risks, you have to sell at the right time. Here's how to figure out when that is: If you're a conservative investor, hang on to your stock as long as it's rising and falling on rumors. Sell a week or two after a firm bid has been made. Reason: By then, the stock price will likely have risen close to the bid, and any remaining profits probably won't offset the risk that the deal could fall apart. If you're an aggressive investor, hang on to your stock a little longer to see if a second potential acquirer appears and makes a better offer. Later bids can add 10% to 15% to the final price. Either way, once you are convinced that all the bids are out, sell your stock, even if the price is 5% to 10% below the bid. Professional investors can earn big bucks holding to the bitter end. But they follow such situations closely and diversify by owning as many as possible. Leave the risky last couple of dollars to the pros.