If you rely on someone else’s income or financially support others, the decision of whether or not to buy life insurance is easy. Determining the right amount to buy is far more difficult, requiring an alchemy of guesswork involving lost income, projected expenses and life expectancy.

In a post at Moneyville, a writer declares that even though he’s tripled the coverage on his policy, he’s still worried he doesn’t have enough.

According to an insurance expert he interviews, the rule of thumb is to buy between 10 and 20 times the amount of your annual income, using a sliding scale for more coverage if you’re younger and less if you’re older. Other guidelines: If you’re a two-income household, try to cover 60 percent of potential lost income over the years, but if you’re a single-income home, insure yourself for 80 percent of the salary.

Mortgages and other forms of debt also come into play. Many people who can afford extra coverage buy enough to make sure loved ones can emerge from a tragedy out of the red.

I tripled my life insurance. Is it enough? [Moneyville]

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