How The Two Estimates Work
The simple needs sum asks what your family would have to pay for without you: the debts, plus the part of your income they live on for the years they need it. Savings and cover you already have are taken off. What is left is the gap. If the answer is negative, you have a surplus on this measure.
The rule of thumb comes from the MoneySense Basic Financial Planning Guide: cover of about 9 times your annual income for death and total permanent disability, and about 4 times for critical illness, while spending at most 15% of income on protection. It is quick, but it knows nothing about your loan, your children or your savings.
Neither number is "the answer". If both point the same way, you can be more confident about the direction. If they disagree, your own figures in the needs sum usually tell you why.