Money Market Calculator
Calculate your money market account earnings, compare MMA vs HYSA vs CD vs Treasury Bills, and optimize your deposits across tiered rate structures. Updated for March 2026 rates.
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How to Use This Calculator
MMA Earnings tab
The default tab. Enter your deposit amount, APY, and time period. The calculator shows total interest earned, monthly breakdown, and comparison to the national average (0.56%). Toggle tiered rates to model banks like CIT Bank that pay different rates at different balance levels.
Compare Accounts tab
Enter the same deposit and compare four options side by side: MMA, CD, HYSA, and Treasury Bills. Select your state to see the Treasury tax advantage — Treasury interest is exempt from state and local income taxes. In high-tax states like California (13.3%) or New York (10.9%), this can make Treasuries the best after-tax option even at a lower headline yield.
Tier Optimizer tab
Enter your bank's tiered rate structure and your current balance. The calculator shows exactly how much more you'd earn by reaching the next tier. See the impact of adding $1K, $5K, $10K, or $25K to your balance.
Share your result
Every input is encoded in the URL. Click Share to send your exact scenario to a partner, financial advisor, or bookmark for later comparison.
The Formula
Money market accounts use compound interest. With APY (Annual Percentage Yield), compounding is already factored in:
Monthly Interest ≈ Balance × ((1 + APY)^(1/12) - 1)
For tiered rates (marginal method):
Total Interest = Tier1 Interest + Tier2 Interest + Tier3 Interest
where each tier applies only to the balance within that range
Treasury Tax-Equivalent Yield = Treasury Yield ÷ (1 - State Tax Rate)
APY vs APR: APY includes compounding, so a 4.00% APY with daily compounding equals roughly 3.92% APR. When comparing accounts, always use APY for an apples-to-apples comparison.
Tiered rates: Most banks use marginal tiers (like tax brackets). The first $10K earns Tier 1 rate, the next $40K earns Tier 2 rate, and so on. Your blended rate is always between the lowest and highest tier.
Example
Lisa — emergency fund optimization in Portland, OR
Lisa has $45,000 in emergency savings sitting in a regular savings account earning 0.35%. She's researching money market accounts and high-yield options. She lives in Oregon (state tax: 9.9%) and wants to maximize after-tax yield without locking up her emergency fund.
MMA Earnings tab
By switching from her 0.35% savings to a 4.00% MMA, Lisa earns $1,800 in her first year — that's $150/month for doing nothing but moving her money.
Compare Accounts tab (Oregon, 9.9% state tax)
In Oregon, Lisa's 3.7% Treasury Bills actually beat a 4.0% MMA after state taxes. The state tax exemption gives Treasury a 4.11% tax-equivalent yield — making it the best after-tax option for her.
Her decision
Lisa splits her $45,000: $20,000 in a high-yield MMA for immediate access (emergency fund needs liquidity) and $25,000 in Treasury Bills via TreasuryDirect for the tax advantage. Total projected earnings: ~$1,650/year after Oregon state tax.