London, May 11: Convention tells us the route to happiness is having children. Yet, a researcher has claimed that marriage without kids is actually the key to bliss.

Prof Daniel Gilbert of Harvard University has said that married life is the key to happiness but having kids can ruin it all, and couples only recover their blissful existence once their offspring have left the nest.

According to him, a desire by couples to get a return on the time and money they have invested in their children is part of the reason they persuade themselves that their offspring are enhancing their lives.

"Figures show that married people are in almost every way happier than unmarried people-whether they are single, divorced, cohabiting. Married people live longer, earn more money per capita, have more sex and enjoy it more," he said.

However, when couples have kids, happiness plummet. "Children do seem to increase happiness (while) you are expecting them, but as soon as you have them, trouble sets in. And happiness returns around the time when children grow up and go away.