Money market deposit accounts

The money market deposit account, or MMDA, was created by the Garn-St. Germain Depository Institutions Act of 1982 as part of the deregulation of bank deposit rates. Its design purpose was to allow banks to compete with money market mutual funds, which had been draining deposits out of the banking system during the inflationary 1970s and early 1980s by offering market-linked yields that bank deposits could not legally match. The MMDA gave banks a deposit product that could pay market-comparable rates, retained federal insurance, and offered limited check-writing — a hybrid of savings and checking designed for the rate-sensitive depositor.

This article describes what an MMDA is today, how it differs from its money-market-mutual-fund cousin, what the tiered-rate structure typically looks like, and where MMDAs sit in a consumer's deposit allocation. For the broader context of deposit-rate setting, see how banks make money; for the related savings product, see savings accounts.

What an MMDA is

An MMDA is a deposit account classified by Regulation D as a savings deposit. Operationally, it differs from a standard statement savings account in three ways: it typically pays a tiered interest rate that varies with the account balance, it typically includes limited check-writing capability (often capped at three to six checks per cycle), and it typically requires a higher minimum balance than a standard savings account, often $1,000 to $25,000.

The tiered-rate structure is the MMDA's defining feature. A typical schedule might pay 4.00% APY on balances below $10,000, 4.25% on balances between $10,000 and $50,000, 4.50% between $50,000 and $250,000, and 4.75% above $250,000 — with specifics varying widely by institution and over the rate cycle. The structure reflects the bank's incentive to attract larger balances; a depositor with $200,000 contributes more to the bank's net interest margin than a depositor with $2,000, and the bank pays a higher rate to compete for the larger deposit.

Like savings accounts, MMDAs were subject to the Regulation D six-transfer limit until April 2020; since the suspension, banks have varied in whether they retain a contractual version of the limit. Many MMDAs continue to limit certain transfer types as a matter of account agreement, and the periodic-statement disclosure under Regulation DD will reflect the actual terms.

MMDA versus money market mutual fund

The MMDA and the money market mutual fund (MMMF) share a name and a general design purpose — to provide a market-rate yield on short-duration money — but are structurally different products with different legal and risk characteristics. The differences are:

• What you hold. An MMDA is a deposit at a bank — a liability of the bank, payable on demand. An MMMF is shares in a mutual fund — equity in a pooled investment vehicle that holds short-duration debt instruments (Treasury bills, commercial paper, repurchase agreements, agency discount notes).
• Insurance. An MMDA is FDIC-insured up to $250,000 per depositor per insured bank per ownership category. An MMMF is not FDIC-insured. MMMFs are registered investment companies regulated by the SEC under the Investment Company Act and Rule 2a-7.
• Net asset value. An MMDA has a balance (in dollars) that can only go up (with interest) or down (with withdrawals); the principal does not fluctuate. An MMMF has a net asset value that, in normal conditions, is managed at $1.00 per share but is not legally guaranteed to remain there. The 2008 Reserve Primary Fund "broke the buck," falling to $0.97; the 2014 SEC reforms required institutional prime money funds to operate with a floating NAV.
• Sponsor. An MMDA is offered by the bank holding the deposit. An MMMF is offered by a mutual-fund sponsor (Fidelity, Vanguard, BlackRock, etc.), held in a brokerage account or 401(k) plan; even when sold through a bank-affiliated broker-dealer, the fund is a separate vehicle and the bank is not the issuer.
• Yield mechanism. An MMDA pays a rate set by the bank, which it can revise at any time. An MMMF distributes its actual portfolio yield (gross of fund expenses) to shareholders; the yield moves continuously with the portfolio's holdings.

The confusion between the two products is widespread and well-earned: the marketing materials often look similar, the historical naming was deliberate (banks chose the name to compete with the funds), and the practical experience of using either is fairly close in normal conditions. The differences become consequential in stress: in 2008, MMDA holders were insured up to the limit while MMMF holders faced the possibility of NAV impairment; in 2023, MMDA holders at SVB were ultimately made whole by the systemic-risk exception while MMMF holders held shares in funds that were never at risk of impairment because the funds invested in Treasury securities rather than bank deposits.

Where MMDAs fit in a deposit portfolio

The MMDA is the rate-tier above a standard savings account at a typical branch-heavy bank: same insurance, same liquidity, modestly higher rate, often with a meaningful minimum balance to qualify for the headline yield. The trade-off relative to a savings account is the higher minimum; the trade-off relative to a CD is liquidity (an MMDA is fully liquid, a CD is not, but the CD typically pays a higher rate for the duration commitment). The trade-off relative to a high-yield savings account at an online-first bank is convenience versus rate; the high-yield savings account often beats the MMDA at a branch-heavy bank on rate, sometimes substantially.

For a depositor at a single branch-heavy bank who wants higher yield without leaving the institution, the MMDA is the typical step up from savings. For a depositor willing to maintain accounts at multiple institutions, the high-yield savings account at an online-first bank often outperforms the same depositor's branch-bank MMDA. The choice is a function of relationship preference, balance size, and rate sensitivity.

Limits and uncertainty

The MMDA as a product category has been stable for forty years. The 2020 Reg D change relaxed the federal transfer-limit constraint; many banks retain a contractual version. The 2023 banking turmoil illustrated, again, the importance of the deposit-versus-investment distinction; MMDA holders at insured banks did not face the dynamics that money market mutual fund holders briefly worried about. Rates on MMDAs vary widely across institutions and over the rate cycle, with the same pattern observed in savings accounts: branch-heavy banks pay materially less than online-first competitors. The product is durable; its competitive position is contested.