What Is a Money Market Fund?

5 min de leitura· Última atualização: 2026-08-14· Pela equipe editorial, revisado com base nas fontes abaixo ·

Resposta rápidaA money market mutual fund is an investment fund that holds very short-term, high-quality debt (like Treasury bills) and pays a yield that moves with interest rates. It is NOT a bank account and NOT federally insured, while a money market deposit account (MMDA) at a bank IS insured like any deposit. The names are nearly identical on purpose-defying levels; the insurance is the difference that matters.

Por que isso importa

When rates are decent, money market funds are where brokerages park cash and often out-yield savings accounts. Knowing the fund/account distinction, and what insurance covers, is the difference between an informed choice and a surprise.

Os passos

Know the two look-alikes

Money market DEPOSIT account: a bank product, FDIC/NCUA-insured within limits, rate set by the bank. Money market MUTUAL FUND: an investment bought through a brokerage, yield from short-term debt markets, not insured.

Know the fund families

Government funds hold Treasuries and government-backed paper (the most conservative flavor); prime funds add corporate short-term debt for slightly more yield; municipal funds trade yield for tax treatment.

Understand the $1 share convention

These funds aim to keep each share worth $1 and pay interest as dividends. Extremely rare stress events ('breaking the buck', 2008) are why regulation tightened; stability is the design goal, not a guarantee.

Match the tool to the job

Emergency fund you must never lose: insured accounts win. Cash at a brokerage waiting to be used, or a yield-chasing cushion beyond the insured fund: a government money market fund is the standard tool.

Same $10,000, three parking spots (illustrative math, not quotes)

Big-bank savings at 0.1% APY$10 interest in a year

High-yield savings at 4.0% APYabout $407 with monthly compounding

Government money market fund yielding 4.5%about $450: uninsured, and the yield floats daily

Erros comuns

Assuming 'money market' means insured. Only the bank deposit version is.
Parking next month's rent in any investment product. Timing risk is real even in conservative funds.
Chasing a prime fund's extra 0.1% for an emergency fund. The safety margin is worth more than the sliver.
Forgetting yields float. Last month's 4.5% is a snapshot, not a promise.

O que fazer a seguir

Compare what your cash earns today using the Interest Rate Comparison tool, then read the full account-types guide before moving anything.

Experimente os cálculos aqui: Interest Rate Comparison The same balance at five different rates, one year and five years out.

Exemplo prático

Balance: $10,000 · Rate 1 (%): 0.1% · Rate 2 (%): 1% · Rate 3 (%): 3% · Rate 4 (%): 4% · Rate 5 (%): 5%

Balance compared$10,000

Gap between 0.1% and 5.0%$501.61 in year one

Rates float; treat these as comparison math, not quotes. The point survives any rate era: the branch-average account and the competitive account differ by real money on the same balance.

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Calculadoras relacionadas

Rate Comparison Compound Savings

Fontes

SEC: Money market funds (Investor.gov) · FDIC: What's covered by deposit insurance