Keeping some of your money, rather than spending it all, generally tops the list of personal finance advice. But where to keep what you accumulate isn’t always as straightforward or obvious. Should you save it, or invest it?

Fortunately, two rules of thumb can help with these decisions: one for emergency funds, and one about your time horizon for using other savings.

Conventional wisdom recommends having 3-6 months of living expenses at the ready, to save you from dire financial straits should you lose your job or face a significant unexpected expense. Because you don’t know when or how quickly you’ll need to withdraw these funds, this money is best stored in the bank, such as a high-yield savings account or in CDs with mild early withdrawal penalties.

If you still have more savings available after funding an emergency account, the standard advice is to invest money you won’t need for five or more years. The reasoning here is that a longer time horizon helps reduce your risk because you’ll likely have time to ride out any market downturns.

Retirement savings are a classic example. Since you won’t use the funds for many years, investing in the market maximizes your opportunity to grow your nest egg. In addition, maxing out what you can put in tax-favored retirement accounts is financially smart, as it shelters as much of your savings from taxes as possible.

For money you expect to use within five years, that decision is the trickiest. If you’ll need the money within a couple of years, keeping it in a bank account is your safest bet. But if you’re saving for a house or large purchase that might take 4-5 years, investing a cautious portion of the funds may help you reach your goal faster.