How quickly should I be able to access my emergency fund?

Your front-line emergency cash should be reachable within a day or two — fast enough to handle a true crisis, but not so instantly accessible that you spend it casually. A high-yield savings account hits that balance: transfers to your checking typically clear in one to a few business days, and many also offer debit or ATM access if you need cash immediately. That's why savings, rather than a CD or invested account, holds the core of the fund — there's no penalty and no waiting period. If you build a deeper second tier in T-bills, CDs, or I-bonds, accept that those are less liquid (I-bonds lock for 12 months; CDs penalize early withdrawal), so they should sit behind a liquid cushion you can tap first. Keep at least a few weeks of expenses where you can reach them almost immediately.