Two accounts at the same bank can pay very different rates on identical balances. The reason is that a bank prices deposits by what they cost to replace and how long they are expected to stay.
Deposits compete with other funding
A bank funds its lending from deposits, borrowings and its own capital. Each source has a price, and deposits are attractive only while they cost less than the alternatives.
When wholesale funding is cheap and plentiful, a bank has little reason to bid aggressively for retail balances. Advertised savings rates fall even though the bank's own lending economics have not changed.
When other funding tightens or becomes expensive, deposits become more valuable and the rates offered on them rise accordingly.
Stickiness is worth more than size
A balance that stays through rate cycles lets a bank lend at longer maturities with confidence. A balance that leaves the moment a competitor posts a better number does not.
Banks estimate this behavior from account history, and checking accounts tied to direct deposit and bill payment tend to be far stickier than standalone savings.
Sticky money is therefore priced cheaply, because it stays regardless, while rate-sensitive money has to be paid for. The rate on an account is partly a statement about how mobile the bank expects that balance to be.
Regulation prices liquidity as well
Supervisory liquidity rules assume different deposit categories run off at different speeds under stress, and require banks to hold liquid assets against the faster ones.
A deposit that regulators treat as likely to flee carries a balance sheet cost beyond the interest paid on it.
That cost feeds into pricing, which is one reason the same institution can value a small insured household balance differently from a large uninsured one.
Branch networks change the arithmetic
Maintaining physical locations and staff is expensive, and that cost is carried by the margin between what a bank earns and what it pays.
Institutions operating without branches have a lower cost base and can pass more of the spread through to depositors while earning the same margin.
This is the structural reason online-only accounts frequently post higher rates than accounts at large branch-based institutions.
Segmentation is deliberate
Banks routinely run legacy accounts at low rates while advertising higher rates on new products, because existing customers move more slowly than new ones shop.
The practice is not an oversight. It reflects a judgment about which balances will move and which will stay if nothing is done.
Understanding it explains why the rate on an account opened years ago is a poor guide to what the same institution currently offers.