Liability-only pays for damage and injuries you cause to other people. It does not fix or replace your own car. Collision and comprehensive, the two parts that make a policy “full coverage”, do, minus your deductible.

The free full coverage vs. liability calculator lets you plug in your car's value, your deductible and the extra premium, and shows how many years of paying for full coverage it takes before the premiums outweigh a total-loss payout.

A few things the number won't tell you:

• If you have a loan or lease, the lender usually requires collision and comprehensive.
• If losing the car would wreck your budget, the extra premium may be worth it even when the math is close.
• Your state's minimum liability limits are often far below a real injury bill. You can check your state's minimums here.

Run your own numbers before your next renewal.