CNNMoney.com provides some tools to help determine your retirement replacement rate.

Researchers recently published a study in the Journal of Financial Planning that provided guidelines for how much you need to save for retirement based on your age and income. The percentages they provide assume you will want to replace 80 percent of your pre-retirement income, except - and this is important - that 80 percent is after deducting the amount you save for retirement.

So, for example, if you earn $80,000 a year and save $10,000, the researchers assumed you would need 80 percent of $70,000, or $56,000 in retirement. The idea is that you don't need to replace the dollars you're saving for retirement since they don't reflect our pre-retirement spending.