If you have never enrolled in a flexible spending account (FSA), you might want to start small. That way you can find out how the FSA works. Depending on the type of FSA, you will want to know which expenses are eligible. Then you can try to estimate what you might expect to pay for the year. Some insurance companies and employers offer estimator tools to help you determine your costs for the coming year. Employers will determine the maximum amount you can contribute to an FSA but it cannot be more than maximum amounts defined by federal tax law.