You may be eligible to contribute up to $3,000 additional past standard contribution limits in a given year if you've worked for your employer for at least 15 years. There's a $15,000 lifetime maximum on this, so if you’re in this situation, you’ll want to keep close track of the amount of extra contributions you make.
Of course, you're not required to contribute this much annually. You may set your own savings rate and adjust it as often as necessary. Usually, you choose what percentage of each paycheck you would like to go toward your retirement, and if your company matches some of your contributions, it will also base its contribution on a percentage of your annual income.
A 403(b) can be a useful retirement savings vehicle. Stay mindful of the rules and fees to help your retirement savings grow as quickly as possible and avoid unnecessary penalties.