Even so, some wealth advisers, who benefit from sales that generate windfalls of cash to invest, are warning clients about the perils of waiting.

Northern Trust Co , one of largest providers of estate and investment advice to multi-millionaires, says a family selling a $70 million business on December 31 would pay $10.5 million in gains taxes. On January 1, that tax bill could jump to as much as $20.2 million.

"That's real money," said Mary Ann Sisco, head of client solutions at Northern Trust's wealth management division.

OBSTACLES

The biggest obstacle to getting a business sold by the end of the year: time. Examining the books of a business for sale and drumming up cash can take prospective buyers six months.

"Unless you're already on the sales block, you're probably out of luck," said Holly Isdale, a former Lehman Brothers and Bessemer Trust adviser who formed Wealthaven LLC in 2010 to counsel ultra-rich families on estate and tax planning.

Many non-financial issues can also scuttle deals. Parents and grandparents, for example, may become emotionally invested in a company and see their business as a legacy they want to pass on to heirs.

"People say 'I've given my life to this company. How can I put a dollar sign on it?'," said Dennis Jaffe, a professor at Saybrook University in San Francisco.

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