Love is...opening a joint bank account with your partner: How merging finances strengthen relationships Researchers found that cohabiting couples who are not engaged have just as strong relationships as those planning to marry - but only if they share an account The study suggests combining financial resources serves as a marker for how determined couples are to make a relationship work. United: The study suggests the real key to a successful relationship may lie in what couples do with their money Never mind bunches of roses, candle-lit dinners or favourite love songs. In the world of romance, nothing says "I love you" more than a joint bank account, according to new research. It shows couples who live together have stronger relationships and feel more committed to each other if they have merged their finances. The findings, published in the Journal of Family Issues, show couples who are cohabiting but not engaged have relationships that are just as strong as those who are planning to marry - but only if they share a joint account. The research, carried out by psychologists at the University of Iowa in the US, suggests combining financial resources serves as a marker for how determined couples are to make a relationship work. The number of unmarried couples in the UK has doubled since the mid 1990s to nearly three million. More than half of first marriages now involve couples who lived together before they got hitched. Relationships where men and women become engaged and plan to wed are generally perceived as more stable than those where there are no long-term marriage plans. But the latest study suggests the real key to a successful relationship may lie in what couples do with their money. Researchers interviewed more than 900 young men and women who were living with their partners. The volunteers were quizzed on the strength of their relationships with questions such as "How likely is that it will be permanent?" or "How committed are you to your relationship"? The results showed that cohabiting couples with joint accounts but no marriage goals were just as happy with the quality of their relationships as those who shared money and had set a wedding date. But couples with separate accounts had lower quality scores. In a report on their findings the researchers said: "They suggest merging finances is associated with higher relationship quality. Joint banking may be an important relationship-building behaviour. Happiness: The results showed that cohabiting couples with joint accounts but no marriage goals were just as happy with the quality of their relationships as those who shared money and had set a wedding date "When couples open a joint account, they are not only more likely to purchase property together but also create a more collective economic unit and a "we" identity." Psychologist Dr Sheila Keegan, from Chiswick in west London, said: "This makes sense. When you're young you have to place a great deal of trust in the relationship. If you keep separate accounts it's like saying you're not quite sure about the relationship yet and want to give it more time. But if you have a joint account it indicates that both partners see it as the first stage in weaving their lives together.