Money Market Account Calculator

A money market account often sits in the practical middle ground between checking and a longer-term savings product: you want the balance to stay accessible, but you also want the rate to matter. This calculator focuses on that exact use case. It grows an existing balance, adds a planned monthly deposit, compounds interest at the frequency you select, and reports the projected future value of the account. The breakdown is intentionally deposit-centered, because a money market account projection can look impressive even when most of the ending balance came from your own contributions rather than interest.

The page is built for bank and credit union money market deposit accounts, not money market mutual funds. A deposit account may be insured within applicable limits when it is held at an insured institution, while an investment fund has a different risk profile. Rates can also be tiered by balance, promotional for a limited time, or changed by the institution. Treat the output as a clean mathematical scenario that you revisit whenever the quoted rate, deposit plan, or time horizon changes.

How to use this calculator

Enter the current starting balance, the monthly deposit you expect to add, an expected annual return, the number of years, and the compounding frequency. The calculator allows annual, quarterly, monthly, and daily compounding. Each deposit is posted at the beginning of its month. The selected nominal compounding convention is converted to an equivalent monthly rate before those cash flows are modeled.

The result panel shows the future value of the money market account, total deposits, total interest, the grown value of the starting balance, the number of compounding periods, and the annual return you entered. Use that separation to ask a sharper question: is the account rate driving the plan, or are recurring deposits doing nearly all the work? If deposits dominate the result, a small rate difference may matter less than choosing a realistic transfer amount. If the starting balance is large, rate differences and compounding choices become more visible.

For nearby comparisons, use the savings calculator for a general savings projection, the compound interest calculator for a broader investment-style compounding model, and the APY calculator when you need to translate a nominal rate and compounding frequency into annual percentage yield. The savings interest rate calculator works in the opposite direction by solving for the rate required to hit a target.

Calculation

The calculator first turns the nominal annual return into the selected periodic rate, then converts that rate to an equivalent monthly rate:

$\text{periodic rate} = \frac{\text{annual return}}{100 \times \text{compounds per year}}$

$\text{monthly rate} = \left(1 + \text{periodic rate}\right)^{\text{compounds per year}/12} - 1$

The number of modeled monthly cash flows is:

$\text{months} = \text{round}\left(\text{years} \times 12\right)$

The starting balance grows with compound interest:

$\text{future starting balance} = \text{starting balance} \times \left(1 + \text{monthly rate}\right)^{\text{months}}$

Deposits are treated as beginning-of-month deposits:

$\text{future deposits} = \text{monthly deposit} \times \frac{\left(1 + \text{monthly rate}\right)^{\text{months}} - 1}{\text{monthly rate}} \times \left(1 + \text{monthly rate}\right)$

When the monthly rate is exactly zero, the calculator uses monthly deposit · months instead of the fraction above. The final account value is:

$\text{future value} = \text{future starting balance} + \text{future deposits}$

Total deposits are tracked separately:

$\text{total deposits} = \text{starting balance} + \text{monthly deposit} \times 12 \times \text{years}$

$\text{total interest} = \text{future value} - \text{total deposits}$

Checking a money market account scenario

Suppose the account starts with $200,000, receives $1,000 at the beginning of each month, earns an expected 0.5% annual return, compounds monthly, and runs for 2 years. The periodic rate is 0.5 divided by 100 and then divided by 12, or about 0.000416667 per month. The number of compounding periods is round of 2 · 12, which is 24.

The growth factor is about 1.0100480634. The starting balance portion therefore becomes $202,009.61. The deposit per period is $1,000, because monthly deposits line up with monthly compounding. Applying the beginning-of-period annuity formula gives future deposits of $24,125.40. Add those two pieces and the projected money market account value is $226,135.01.

Total deposits are the original $200,000 plus $24,000 of new contributions, or $224,000. Total interest is $2,135.01. That distinction matters: in this low-rate example, almost all of the ending balance is principal. A higher rate, a longer period, or a larger opening balance would make the interest share larger, but the calculator will still show the deposit and interest components separately.

How to interpret the result

Use the projection as a planning snapshot. If the balance is for an emergency fund, the most important question may be whether the ending value keeps pace with your target cash reserve, not whether it beats every available yield. If the balance is for a near-term purchase, test a few conservative rates so the plan does not depend on a promotional APY staying in place. If the account has balance tiers, run the calculator at the tier you expect to occupy most of the time rather than the highest advertised tier.

Money market accounts are frequently compared with high-yield savings accounts, CDs, Treasury bills, and cash management accounts. The calculator does not rank those options because access, insurance, penalties, and rate variability are different. A CD may lock a rate but limit early access. A savings account may have fewer transaction features. A Treasury security has its own tax and maturity treatment. This page simply answers the MMA balance question using the exact compounding and deposit assumptions entered in the inputs.

Caveats and common mistakes

• Do not assume the rate is guaranteed. Money market deposit account rates can change after you open the account.
• Do not ignore fees or balance requirements. A small monthly fee can erase much of the interest on a modest balance.
• Do not compare a quoted APY with a nominal rate unless you understand whether compounding has already been included.
• Do not use this page for a money market mutual fund without checking the fund’s yield convention, expenses, and risk disclosures.
• Do not mix time periods. A monthly deposit should be the amount you can actually add each month for the entire entered period.

Method scope and source version

Jurisdiction-neutral arithmetic; accounting, contractual, market, or institutional conventions may vary. Evergreen method only; defaults/examples must not be represented as current market, legal, tax, or institutional data. The sources below support the stated method and definitions; they do not supply a live rate, quote, legal conclusion, lender offer, or institution-specific policy.

Sources

• CFPB, What is a money market account? — consumer explanation of money market deposit accounts and how they differ from other products.
• CFPB, What is an annual percentage yield? — definition of APY as a rate measure that includes compounding.
• FDIC, Deposit insurance resources — overview of deposit insurance coverage for eligible bank deposit accounts.