Mixing APY and APR
APY already reflects compounding. Do not compound an APY as if it were a simple nominal APR unless the page clearly asks for a nominal rate.
Savings calculator
Money Market Calculator
Estimate how a money market account balance could grow from an opening deposit, monthly additions, APY, and time. This money market calculator is the practical tool for money market calc, money market calculator, and money market account calculator intent, while the separate guide explains the formula and interpretation in plain language.
Updated: July 5, 2026
Calculate money market growth
Estimated ending balance—
Total deposits—
Estimated interest earned—
Live APY scenario comparison
Lower APY—
Current inputs—
+$100 monthly deposit—
Deposit vs interest breakdown
This insight updates to compare deposits with estimated account interest.
Total deposits—
Estimated interest—
Money market calculator formula
The calculator treats the entered APY as the annual yield and converts it into an equivalent monthly rate. It then compounds the balance monthly and adds the monthly deposit at the end of each month.
If you are here to understand the formula rather than run a scenario, the companion guide how to calculate money market interest walks through the same APY conversion logic step by step.
Monthly rate = (1 + APY)^(1/12) - 1
Ending balance = monthly compounding of opening deposit plus each monthly deposit
Worked example: money market account with monthly deposits
Suppose a money market account starts with $10,000, receives $250 per month, and uses a 4.25% APY for 12 months. The calculator compounds the existing balance each month, adds each monthly deposit, and separates the estimated interest from the cash you contributed.
Now compare that base case with a lower APY scenario or a higher monthly deposit scenario. If a small APY change meaningfully reduces the ending balance, the estimate is rate-sensitive. If adding another $100 per month matters more than the APY change, contribution size is doing more of the work than yield alone.
How to interpret the estimate
Estimated ending balance is the projected balance under the entered assumptions. Total deposits combines the opening deposit and monthly additions. Estimated interest earned is the difference between the ending balance and deposits before taxes, fees, or account-specific adjustments.
If a money market account has a variable APY, use several rates rather than one fixed number. A lower-rate scenario can show what happens if rates fall, while a higher-deposit scenario can show whether contributions matter more than yield over the chosen period.
This is the main value of a money market calculator: it helps separate projected earnings from your own deposits. If the ending balance looks strong mainly because you are adding cash every month, that is different from an account where the APY itself is producing most of the gain.
What this estimate excludes
- Tiered APYs that change when the balance crosses a threshold.
- Monthly maintenance fees, transaction fees, or fee waivers.
- Promotional rates that expire before the selected term ends.
- Taxes on interest, withdrawal limits, transfer timing, and institution-specific rules.
- Changes in APY after account opening.
Common money market calculation mistakes
Ignoring balance tiers
Some accounts advertise a top APY only for certain balances. Use the rate that matches the balance and disclosure you are comparing.
Treating rates as fixed
Money market rates can change. Run lower-rate scenarios before relying on a one-year projection.
Next steps
Use the APY comparison calculator to compare two yield offers, the compound interest calculator for broader contribution scenarios, and the savings goal calculator when you are working toward a target amount. For formula background, read how to calculate money market interest. For rate terminology, review APR vs APY explained. If the same cash may later be used for drawdown planning, continue to the savings withdrawal calculator.
Method and verification trail
- Method used: The entered APY is converted into an equivalent monthly growth rate, then applied to the opening deposit while monthly additions are added after each monthly compounding step.
- Primary source type to verify: Account disclosures, APY sheets, balance-tier terms, fee schedules, and provider statements for any money market account being compared.
- What to verify in real documents: Whether the quoted figure is APY or a temporary rate, whether balance tiers or fees apply, whether the APY can change during the term, and whether contribution timing matches how you expect to use the account.
- Scope limit: This page does not model taxes, changing APYs, transaction limits, promotional expirations, insurance rules, or institution-specific posting schedules.
For site-wide methodology, review How We Calculate. For sourcing and corrections standards, review Editorial Policy.
FAQ
Is this a money market account recommendation?
No. The calculator only estimates growth from the numbers entered. It does not compare institutions, rank accounts, or recommend a product.
Does the calculator use APY or APR?
It uses APY. The entered APY is converted into an equivalent monthly growth rate so the result is consistent with an annual percentage yield.
Can this calculator estimate a money market account with monthly deposits?
Yes. It combines the opening deposit, monthly additions, APY, and time period to estimate ending balance and interest earned in a simplified scenario.
Are money market rates guaranteed?
Not necessarily. Many money market account rates are variable and can change over time. Check the current account disclosure for actual terms.
Does the estimate include taxes or fees?
No. Taxes, fees, minimum-balance rules, and transfer limits are excluded because they vary by account and user situation.
Scenario comparison checklist
Money market projections are most useful when the inputs are tied to real account terms. Compare a lower APY, the advertised APY, and a higher monthly deposit before deciding which input drives the estimate. If the account has fees or rate tiers, subtract those separately or test a lower effective rate.
- Confirm that the rate is APY, not APR or a temporary promotional rate.
- Check minimum balance and fee rules before treating the interest estimate as net growth.
- Use the term that matches how long the money may remain in the account.
- Keep emergency cash, savings goals, and longer-term investments conceptually separate.
Related guides
Read how to calculate money market interest for the step-by-step formula and interpretation, or review APR vs APY explained if rate terminology is unclear.