Find Interest Rate Arbitrage Opportunities
The US savings rate landscape in 2026 is the most rewarding it's been in 15 years — and most Americans are still leaving thousands of dollars on the table. As of late spring 2026, the leading high-yield savings accounts (HYSAs) are paying north of 4.30% APY: Marcus by Goldman Sachs and SoFi Checking & Savings both sit at 4.50%, Wealthfront Cash holds 5.00%, and Apple Savings offers 4.35%. On the brokerage side, money market funds (MMFs) like Vanguard's VMFXX yield roughly 5.20% (7-day SEC yield) and Fidelity's SPAXX hovers near 5.00%. Bank CDs run 5.00–5.25% APY for 12-month terms and ~4.50% for 5-year ladders. Treasury Bills auctioned through TreasuryDirect pay ~5.30% at the 4-week tenor and ~5.10% at 26 weeks, with the bonus of being exempt from state and local income tax. Series I Bonds are at a composite rate of ~4.28% for the Nov 2025–Apr 2026 issue. Meanwhile, the average Chase or Bank of America checking account still pays 0.01% APY. That is not a typo. Leaving $10,000 idle in a 0.01% account costs you roughly $500 a year compared to a 5.00% HYSA — a pure inertia tax. This calculator surfaces that spread instantly so you can decide whether moving cash is worth it.
When to use this calculator
- Move $20,000 idle in a Chase or Bank of America 0.01% checking account into a Marcus 4.50% HYSA and see the exact annual gain ($898/yr).
- Build a $50,000 emergency fund Treasury Bill ladder (4/8/13/26-week rungs) and compare it head-to-head against a single-rate HYSA.
- Park $100,000 of taxable brokerage cash in Vanguard VMFXX at 5.20% vs leaving it as cash sweep at 0.50% — and quantify the tax-adjusted edge.
- High-tax state residents (CA, NY, NJ): compare a 5.10% T-Bill (state-tax-exempt) against a 5.25% HYSA after California's 9.3% state income tax bite.
- Decide whether to break a 4.25% bank CD early to reinvest in a 5.20% brokered CD, after accounting for the 3-month early-withdrawal interest penalty.
- Pre-retirement: stagger a $250,000 CD ladder across Marcus, Synchrony, and Fidelity brokered CDs and compare blended yield to a single 5-year jumbo.
Calculation Example: Chase Checking vs Marcus HYSA
- Account A (Chase checking): 0.01% APY
- Account B (Marcus HYSA): 4.50% APY
- Principal: $20,000 — Term: 365 days
- Spread = 4.49 percentage points; annual gain ≈ $898
How it works
4 min readCash that sits idle at 0.01% APY is the single most expensive habit in US personal finance right now. With risk-free yields above 5% on Treasury Bills and money market funds, the spread between a lazy bank account and an optimized cash position has never been wider in modern memory. This calculator helps you size the opportunity in dollars and decide whether the move is worth it.
APR vs APY — Why the Disclosure Matters
Under Regulation Z (Truth in Lending) and Regulation DD (Truth in Savings), US banks must disclose APR (nominal annualized rate, no compounding) on loans and APY (annual percentage yield, includes compounding) on deposits. For deposits, APY is the apples-to-apples number — a 4.40% APR compounded daily is roughly 4.50% APY. Always compare APY across HYSAs, MMFs, CDs, and T-Bills (using bond-equivalent yield) — never compare APR to APY.
Money Market Funds vs HYSAs
A HYSA like Marcus, SoFi, Ally, or Wealthfront is a deposit account at an FDIC-insured bank — protected up to $250,000 per depositor, per insured bank, per ownership category. A money market fund (MMF) like Vanguard VMFXX or Fidelity SPAXX is a mutual fund, not a bank account. MMFs are NOT FDIC-insured, but they invest almost exclusively in T-Bills, government repos, and short-dated agency paper — effectively near-Treasury risk. In 2026 the top MMFs yield about 0.30–0.70 percentage points more than the best HYSAs (5.20% vs 4.50%), which is real money on six-figure balances. For most savers, a hybrid works: HYSA for emergency cash, MMF inside a brokerage for taxable surplus.
CD Ladders: 12/24/36/48/60 Month
The classic ladder splits your CD allocation across five rungs so one rung matures every year, restoring liquidity without forcing you to predict rates. In 2026 the yield curve is mildly inverted on the front end (12-month CDs at 5.00–5.25% vs 60-month at ~4.50%), which makes a barbell (heavy short + heavy long, skip the middle) or a short-focused ladder more attractive than the textbook even ladder. Always compare to brokered CDs on Fidelity or Schwab, which often beat local bank CDs by 30–60 bps and provide a secondary market if you need early liquidity.
Treasury Bills — The State Tax Edge
T-Bills auction weekly at TreasuryDirect.gov (no broker, no commission) at 4-week, 8-week, 13-week, 17-week, 26-week, and 52-week tenors. Current yields: ~5.30% (4-wk), ~5.20% (13-wk), ~5.10% (26-wk). The crucial advantage: interest is exempt from state and local income tax. For a California resident in the 9.3% bracket, a 5.10% T-Bill is equivalent to a 5.62% HYSA on a pre-tax basis. New York City residents (combined ~10.9% state+city) get even more benefit. Vanguard, Fidelity, and Schwab also let you buy T-Bills at auction or in the secondary market with zero commission.
Series I Bonds — Inflation-Linked
I-Bonds (TreasuryDirect.gov) blend a fixed real rate with a semiannual inflation adjustment. The Nov 2025–Apr 2026 composite is ~4.28%. Limits: $10,000 per Social Security Number per calendar year (plus $5,000 via tax refund). Constraints: must hold 1 year minimum; if redeemed before 5 years, you forfeit the last 3 months of interest. Interest is federal-only (no state tax) and deferred until redemption — and if used for qualified higher-education expenses subject to AGI limits, it can be federal-tax-free too.
Money Market Account (MMA) vs HYSA
Don't confuse a money market account (MMA, FDIC-insured bank product with optional check-writing) with a money market fund (MMF, brokerage mutual fund). MMAs typically pay slightly less than the best online HYSAs but add check-writing or debit-card access. For pure yield, an online HYSA wins.
Brokered CDs vs Bank CDs
Fidelity, Schwab, and Vanguard offer brokered CDs aggregating 200+ banks on one platform. Advantages: usually 20–60 bps higher than local bank CDs, FDIC-insured up to $250k per issuing bank (you can stack across multiple issuers in one brokerage account for jumbo coverage), and a secondary market if you need early liquidity (subject to price risk — not a guaranteed return of principal like a bank CD penalty).
Tax Implications by Account Type
The Cost of Inertia
Most Americans don't move their savings. Bank of America, Chase, and Wells Fargo collectively hold trillions in 0.01% APY deposits — a stunning quantity of unrealized yield. The behavioral finance term is inertia or status quo bias. At 5% spreads, $20,000 of inertia costs $1,000/year. $50,000 costs $2,500/year. That's not a rate-of-return calculation — that's a free dinner, every week, that you're not eating.
When Arbitrage is NOT Worth It
Important Disclaimers
Rates change weekly. APYs quoted are accurate to late spring 2026 but verify directly on each provider's site before transferring. FDIC and SIPC limits apply at the institution level — if you hold more than $250k at one bank, consider splitting across multiple insured institutions. This calculator is not investment advice; for tax-sensitive decisions (Roth conversions, I-Bond strategy, jumbo CD ladders), consult a CFP or CPA.
Frequently asked questions
Is moving to an HYSA actually worth it?
Almost always, yes. The median Chase or Bank of America savings account pays 0.01% APY; Marcus, SoFi, and Wealthfront pay 4.50–5.00% APY. On a $20,000 balance that's roughly $900/year of free yield. ACH transfer is free, account opening takes 5 minutes online, and FDIC coverage up to $250k is identical to any other US bank.
Money market fund (MMF) vs HYSA — which is better?
MMFs (Vanguard VMFXX ~5.20%, Fidelity SPAXX ~5.00%) typically yield 30–70 bps more than the best HYSAs (Wealthfront 5.00%, Marcus 4.50%). MMFs are not FDIC-insured but invest in T-Bills and government repos — effectively near-Treasury risk. Use an HYSA for emergency cash you might need same-day; use an MMF inside a brokerage for taxable surplus parked for weeks or months.
Are Treasury Bills really state-tax-exempt?
Yes. T-Bill interest is exempt from state and local income tax under federal law (31 U.S.C. § 3124). Only federal income tax applies. For a California resident in the 9.3% state bracket, a 5.10% T-Bill has the same after-tax yield as a 5.62% HYSA. The savings compound for high earners in NY, NJ, OR, MA, and CA.
How does a CD ladder work in 2026?
Split your CD allocation into 5 equal rungs maturing in 12, 24, 36, 48, and 60 months. Each year a rung matures and you can either use the cash or reinvest at the longest tenor. With the 2026 yield curve mildly inverted, a barbell (heavy 12-month + heavy 60-month, skip middle) or a short-focused ladder often beats the textbook even ladder. Always check Fidelity or Schwab brokered CDs vs your local bank — brokered usually wins by 20–60 bps.
Why is the I-Bond limit only $10,000 per year?
It's a Treasury cap: $10,000 per Social Security Number per calendar year via TreasuryDirect, plus up to $5,000 extra by directing a federal tax refund to I-Bonds. The cap is per-person, so a married couple can buy $20,000 (plus $5,000 each via refund). I-Bonds must be held 1 year minimum, and redeeming before 5 years forfeits the last 3 months of interest.
Brokered CD vs bank CD — what's the difference?
A bank CD is bought directly from a bank with a fixed early-withdrawal penalty (typically 3–12 months of interest). A brokered CD is bought through Fidelity, Schwab, or Vanguard — they aggregate 200+ banks, usually offer rates 20–60 bps higher, and you can sell on the secondary market if you need liquidity (subject to price risk). FDIC insurance applies at the issuing bank level in both cases, so brokered CDs let you stack coverage across multiple banks within one brokerage account.
Are HYSA promotional bonus accounts worth the hop?
Sometimes. SoFi, Chase, Wells Fargo, and Citi periodically run $200–$400 bonuses for new checking/savings accounts with direct-deposit requirements. On a $5,000 minimum balance, a $300 bonus is a 6% one-time yield boost — meaningful. But factor in the time to open, the early-closure clawback (usually 6 months), and the soft credit pull. Stack with a high-yield HYSA elsewhere — don't park long-term savings in a bonus account paying 0.50% APY.
What happens to my FDIC coverage if a bank fails?
The FDIC insures up to $250,000 per depositor, per insured bank, per ownership category (individual, joint, IRA, trust). If your bank fails, the FDIC typically resolves it over a weekend — you have access to insured funds by Monday, usually as an account at an acquiring bank. Online HYSAs at Marcus, Ally, Capital One, Discover, SoFi, Wealthfront (via partner banks) all carry standard FDIC coverage. For balances above $250k, split across multiple insured institutions or use brokered CDs to stack coverage.
Do I have to pay quarterly estimated taxes on HYSA or T-Bill interest?
Potentially. If you expect to owe more than $1,000 in tax for the year and your withholding won't cover at least 90% of current-year or 100% of prior-year tax (110% if AGI > $150k), the IRS requires quarterly estimated payments (April 15, June 15, Sept 15, Jan 15). At 5% APY, $50,000 generates $2,500 in taxable interest — at a 24% federal bracket, that's $600. Add state tax for HYSA/CD/MMF (T-Bill state-exempt). Check IRS Form 1040-ES or talk to a CPA.