Social security benefits make up 80% of most workers retirement income, according to Sita Nataraj Slavov, a professor at George Mason University’s Schar School of Policy and Government. As a result, knowing how much you will receive in Social Security benefits is important for planning when and how to retire.

The Social Security Administration issues estimates, but their calculation assumes you will continue earning and paying the same amount of social security taxes until you begin claiming benefits. This can erroneously boost projected benefits for those who stop working or have a dip in their income.

How can you get a more accurate number for planning purposes? The Social Security Administration’s website has a retirement benefit planner for you to enter your past and future expected earnings year by year and receive a more refined projection online.

Social Security benefits are adjusted on a monthly basis, increasing each month the claim is delayed from the full retirement age. The average worker’s Social Security benefit increases by about 8% for each year they delay claiming benefits from their full retirement age until reaching the maximum available benefit at age 70.

Many retirees waiting to begin collecting benefits until age 70 need a plan for funding their living expenses during the interim period. The average age when retirees claimed Social Security benefits was 64.5 for men and 64.3 for women in 2016, according to the Social Security Administration.

Part of the equation is related to life expectancy. According to the Social Security Administration’s Life Expectancy Calculator, 65 year-old men can expect to live until age 84.2 and 65 year-old women are expected to reach 86.7 years of age, on average. But, the older one gets, the longer they can expect to live. 70 year-old men can expect to reach 85.7 and 70 year-old women 87.7 years.

It is advantageous to wait until 70 to claim social security benefits because higher benefits provide better protection against running out of money for those who live longer than average versus claiming benefits earlier. Although doing so requires enough savings to cover living expenses until social security benefits begin, tapping savings is often worthwhile for this purpose.