Many experts recommend you should save 10 to 15 percent of your pre-tax income each year for retirement. However, they come to that figure by making assumptions that may not be accurate for you. Here are ways that you can make a better estimation of your retirement needs by using your personal data.

When it comes to retirement savings, it literally pays to start early. Often expert calculations assume that you will save for retirement from ages 25 to 67. If you start saving at a later age or plan to retire at an earlier age, you need to save more than 15 percent annually. For example, Fidelity projects that someone who begins saving for retirement at age 35 needs to save 23 percent annually.

One way to lower the amount you’ll need to put aside is to work past age 67. Shortening your retirement by working longer reduces how much you need to save. You also get the added benefit of increased monthly benefits from Social Security after age 67.

There’s another way figure out your retirement savings rate. First, tally your current expenses for a typical month. Next, subtract any expenses that you won’t have during retirement such as childcare or your mortgage. Finally, add expenses you don’t have now but you will have during retirement. Think about how you’re going to spend your time in retirement to come with the additional retirement expenses. If you’re planning to travel often or take up an expensive new hobby, be sure to include those costs.

Multiply your estimated monthly retirement expenses by twelve to approximate how much you need each year during retirement. Finally, take the annual estimate you calculated and figure what percent of your current yearly income it represents. Experts refer to this percentage as your income replacement ratio, which tells you what percent of your pre-retirement income you need to keep your lifestyle.

To see how this works, look the example of a fictional worker named Robert who has $5,000 in monthly expenses now. After subtracting his commuting costs and mortgage, $3,400 was left. Adding another $100 for recreational activities during retirement brings his estimated monthly retirement expenses to $3,500. Robert estimates that he’ll need $42,000 annually during retirement, which is 70 percent of his current $60,000 salary.

Retirement seems like a ways away; however, it’s within best practices to start preparing as soon as possible to make your transition smooth and simple.