What This Calculator Simulates
The tool runs your money market account forward one month at a time, the same cadence a bank statement uses. You start with an opening deposit, add what you plan to contribute each month, and set a horizon of up to 600 months. Every month the simulation charges any applicable fee, credits interest, adds the deposit, and moves on — a structure close to how a real account behaves over a year of statements.
Two rate fields matter because most money market accounts pay tiered rates. The base APY applies to the balance below the threshold you enter; the tier APY applies only to dollars above it. A $50,000 balance in the default setup earns 4.1% on the first $25,000 and 4.6% on the rest, which blends to 4.350% — the number worth quoting when you compare offers.
The default run starts at $10,000, adds $500 monthly, and runs 36 months. It finishes at $30,387.76 with $2,387.76 of interest credited on $28,000 of deposits, an annualized net yield of 4.04% on an average balance of $19,702.53. Those two last figures are the honest ones: yield measured against what you actually kept in the account, after every fee.
Tiered Rates and Your Blended APY
Banks quote tiered rates because they want larger deposits, but the headline number only touches the top slice. With the default 4.1%/4.6% split at $25,000, a $30,000 balance blends to 4.183%, $50,000 blends to 4.350%, and $100,000 to 4.475%. Compare the blended column against a flat savings rate — anything else flatters the tiered account.
In the default run the balance crosses $25,000 in month 28, so the top tier pays for only nine of the 36 months. That late crossing costs real money: the tier adds just $8.74 versus a flat 4.1% APY over the full period. Front-load the deposits and the crossing happens sooner — at $1,000 per month the balance clears the threshold in month 16, and the tier bonus grows to $103.30.
This is why two accounts quoting the same top rate can pay differently. An account paying 4.6% above $10,000 beats one paying 4.6% above $50,000 for every balance in between. The APY calculator breaks down how a quoted APY converts into a monthly rate; run both offers through this tool and compare ending balances rather than sticker rates.
Minimum Balances and the Fee Trap
Most money market accounts charge a monthly maintenance fee when the balance sits below a minimum — $10 below $2,500 is a common structure. The simulation charges that fee at the start of every month the balance is under the line, before interest credits. Fees compound against you the same way interest compounds for you.
Start with $2,000, deposit $100 monthly, and the numbers turn ugly fast: over one year the account pays $102.47 of interest, loses $60 to fees, and nets $42.47 — a 1.67% effective yield on a 4.1% advertised rate. Drop the monthly deposit to zero and the account ends below where it started, with $79.35 of interest against $120 of fees for a net loss of $40.65.
The fix is structural, not promotional. Either keep the balance safely above the minimum or move the cash to an account with no floor — many online savings accounts dropped minimums entirely. If an occasional dip is likely, price it here first; a fee that triggers three or four times a year can quietly erase a quarter-point rate advantage.
Money Market, Savings, or CD?
A money market account is a deposit account: FDIC insured at a bank, check-writing privileges in many cases, and a variable rate. A high-yield savings account is the same plumbing without the checks, usually at one flat rate. A certificate of deposit trades liquidity for rate certainty — the APY locks, early withdrawals cost penalties, and the fixed deposit calculator prices that lock-in structure.
Tiers are the money market account's edge. Savings rates are typically flat, so a $60,000 deposit earns the same rate per dollar as $6,000. The tiered structure in the default setup blends to 4.433% at $75,000 — roughly a third of a point above its own base rate. On the default 36-month run the tiered account beats a flat 4.1% savings account by $8.74, and the gap grows to $133.73 at 60 months as the balance spends more time above the line.
For money with a known date — a house down payment, tuition, a tax bill — a CD usually wins, and a future value calculator projection of the locked rate makes the comparison concrete. For money that needs to move, the MMA's mix of yield and access fits better. Use the compound savings calculator to sanity-check the same deposit schedule at a flat rate before committing.
Rate Shopping With Real Numbers
Advertised rates move fast, so the tool prices the full spread. Holding everything else at the defaults, a flat 3.1% APY grows $28,000 of deposits to $29,785.19 over 36 months; 4.1% reaches $30,379.02; 5.1% reaches $30,981.58. Each point of APY is worth roughly $600 on this deposit pattern — real money, but small next to what a fee or a missed tier can do.
Tier gaps matter less than the marketing suggests. Widening the top tier from 4.6% to 5.1% on the default run adds $17.48 over 36 months; widening it to 5.6% adds $26.20. Only the dollars above $25,000 earn the higher rate, so early in the accumulation phase the base rate and the fee schedule do the heavy lifting.
When two offers differ in both rate and structure, run each through this tool with identical deposits and compare the ending balances — that single figure absorbs tiers, fees, and compounding differences at once. The interest rate calculator works the other direction, solving for the rate when you already know the interest a quote produced.
APY, 7-Day Yield, and Variable Rates
APY already includes the effect of compounding, which is why this tool converts it to a monthly factor with (1 + APY)^(1/12) - 1 rather than dividing by 12. A 4.1% APY compounds to about 0.335% per month, not 0.342%. Comparing an APY against a nominal rate understates the APY side, so always line up APY against APY.
Money market funds — mutual funds, not bank accounts — quote a 7-day yield, an annualized snapshot of the trailing week. Bank money market accounts quote APY. The two numbers are close cousins but not identical, and the comparison that matters for a bank MMA is APY versus APY. Rates on both move with the policy rate, so a 4.6% quote today is a variable promise, not a contract.
Inflation is the silent line item. The default run's $30,387.76 ending balance has the buying power of $28,218.06 at 2.5% average inflation, or $27,809.11 at 3%. The inflation calculator converts any ending balance into today's dollars; on long horizons the real yield is the honest scoreboard.
Deposit Strategy Around the Threshold
The deposit sweep shows how much the pattern matters. At $0 monthly the default account ends at $11,281.15 after 36 months; $250 monthly ends at $20,830.09; $500 at $30,387.76; $1,000 at $49,580.14. The jump from $250 to $1,000 in deposits nearly doubles the interest earned — $1,830.09 becomes $3,580.14 — because the balance spends its final months above the threshold.
Front-loading exploits the same effect. Moving $15,000 into the account at month one instead of spreading it across the year pushes the crossing month from 28 into single digits and lets the tier rate work for the whole horizon. The cost of waiting is not the missed base interest alone; it is every month the top tier pays $0 on the balance you plan to build anyway.
Pair this tool with the savings goal calculator when the target is a number rather than a date: it backs out the monthly deposit needed to hit, say, a $30,000 emergency fund, and this calculator verifies what that schedule actually earns once your account's tiers and fees enter the picture.
Where the Account Fits Your Cash Plan
A money market account earns its keep as the liquid tier of a cash plan — the money between daily checking and long-term investments. The emergency fund calculator sizes that tier in months of expenses; three to six months of spending parked in a tiered MMA earns yield without giving up access when the car dies or the job pauses.
Bank money market deposits carry FDIC insurance up to the standard $250,000 limit per depositor, per bank, per ownership category — balances above that spread across institutions. The federal six-transfer-per-month rule from Regulation D was suspended in 2020, but many banks still set their own transaction caps, so check the account agreement before routing bill payments through the account.
Interest is taxable as ordinary income in the year it credits, so a $2,387.76 interest run adds real tax at your marginal rate. Track the account inside the liquid net worth calculator to keep the liquid share of your net worth honest, and revisit the compound interest calculator when a rate change shifts the math. Re-run this tool whenever your bank reprices — the answer moves.