Picture $150,000 sitting in a business checking account earning 0.10% APY. Over a year, that's $150 in interest — less than the cost of the coffee your team drinks on a single Monday. Move that same balance into a treasury sweep account paying 4.3%, and it becomes $6,450. Same cash, same risk tolerance, thirteen months of runway extended into fourteen or fifteen, just by choosing a different account structure.
That gap is why "treasury management" — once a phrase reserved for CFOs at companies with finance departments — has become a marketing headline for fintechs like Mercury, Rho, Arc, and a growing list of neobanks courting small businesses and startups. The pitch is simple: keep your operating cash where you already bank, but automatically sweep the excess into something that actually earns a return. The reality is more nuanced, and the fine print on insurance coverage is where most business owners get surprised.
What "Idle Cash" Actually Means
Every business carries a buffer above its immediate operating needs — payroll runway, a tax reserve, a rainy-day fund for a slow month. That buffer is supposed to sit there, not be invested in anything volatile. The problem is that "safe" and "earning nothing" got conflated for over a decade of near-zero interest rates, and a lot of business owners never revisited the assumption once rates moved.
If you're holding six figures in a checking account that pays fractions of a percent, that's not caution — it's an unforced cost. The question isn't whether to earn a return on cash reserves; it's which vehicle keeps that cash exactly as safe and exactly as liquid as it needs to be while doing so.
The Traditional Option: A Business Savings Account
A standard business savings account is the familiar choice: open it at your bank, funds transfer over in a day or two, and it earns whatever your bank posts — often a token rate at a national brand, though online-only banks and credit unions are considerably more competitive. High-yield business savings accounts from banks like Axos, Live Oak, and various credit unions are currently paying in the 3.25%–3.75% APY range, with tiered products at some institutions crossing 3.75% APY on larger balances.
The upside is simplicity and familiar FDIC protection: up to $250,000 per depositor, per bank, through ordinary deposit insurance. The downside is the ceiling. Most business savings accounts cap monthly transactions (a holdover regulation many banks still enforce informally even after the Fed relaxed Regulation D), and yields — while much better than checking — still trail what treasury and money-market products can offer, particularly for balances well above the FDIC limit.
The Fintech Option: Treasury and Sweep Accounts
This is where Mercury, Rho, and similar platforms have built a real differentiator. Instead of a single account with a single rate, they offer a tiered cash management structure — typically an operating account for day-to-day spend, plus a treasury or "reserve" tier that automatically routes excess balances into short-term government securities or money market funds.
How it actually works:
- Treasury accounts invest idle balances in Treasury bills, money market funds, or similar low-risk instruments, often yielding above 4% APY depending on prevailing rates. Mercury Treasury, for example, has advertised yields in that range by holding U.S. government securities and money market funds — but that money is invested, not deposited, so it's typically covered by SIPC (Securities Investor Protection Corporation) up to $500,000, not FDIC.
- Sweep networks work differently: instead of investing your cash, they distribute it across a network of partner banks in increments under $250,000 each, so the whole balance stays FDIC-insured. Rho's sweep network, run through partners like the American Deposit Management Co., can extend FDIC coverage into the tens of millions of dollars by spreading deposits across 400+ banks. Mercury offers a similar sweep structure providing up to $5 million in FDIC coverage. The tradeoff: sweep-network cash sometimes earns little to no interest on its own, so many platforms pair it with a separate interest-bearing treasury product for the yield.
That distinction — invested-and-SIPC-insured versus swept-and-FDIC-insured — is the single most important thing to understand before moving six or seven figures anywhere. They solve different problems: one maximizes yield, the other maximizes deposit protection on a large balance.
Treasury Bills, in Plain English
A lot of the yield behind these accounts ultimately traces back to Treasury bills — short-term U.S. government debt maturing in 4, 13, 17, 26, or 52 weeks. You buy a T-bill at a discount to its face value and get the full face value back at maturity; the difference is your return. Buy a $1,000 T-bill for $980 and collect $1,000 at maturity, and you've earned roughly 2% over that bill's term, annualized out to whatever the current rate implies.
T-bills carry essentially zero default risk — they're backed by the full faith and credit of the U.S. government — but they aren't riskless in every sense. If you need the cash back before maturity and rates have risen since you bought in, selling on the secondary market can mean taking a small loss on principal. That's a minor concern for a 4-week bill and a real one for a 52-week bill, which is why treasury sweep products for small businesses typically ladder short-duration bills rather than locking cash away for a year.
Run the math on a modest reserve: $50,000 sitting in a checking account effectively earning nothing over a year returns almost nothing. The same $50,000 in a well-managed T-bill ladder or treasury account at 4.3%–4.7% generates somewhere in the neighborhood of $2,000–$2,300 a year — a meaningful line item for a small business, not just rounding error.
What to Weigh Before Moving Money
Minimum balances and fees. Sweep and treasury products often make the most sense above $100,000–$250,000 in reserves — below that, a straightforward high-yield savings account may net out similarly after fees, and some treasury tiers carry account minimums in that range or higher. Management fees on treasury products typically run from about 0.10% to 0.60% annually; at scale, a 50-basis-point difference matters.
Liquidity needs. If you might need the full balance back inside a week — say, a supplier payment or a tax deadline — confirm settlement time. Sweep accounts across partner banks are usually available quickly; T-bill ladders can take a business day or two to unwind depending on the maturity structure.
Insurance type, not just insurance amount. "FDIC-insured up to $5 million" and "SIPC-insured up to $500,000" protect against different failure modes and aren't interchangeable. Ask specifically which of your balances sit in each bucket — reputable providers disclose this in their account terms, and it's worth reading rather than assuming.
Concentration risk on the platform itself. A sweep network protects you if one of the partner banks fails. It does less to protect you if the fintech itself — the layer between you and the sweep network — has an operational or business failure. Regional bank stress in recent years is a reminder that "who actually holds my money, and through what agreement" is worth knowing before there's a crisis, not during one.
Reconciliation overhead. A treasury or sweep product introduces monthly interest income, sometimes across several underlying partner banks, that needs to hit your books correctly — as interest income, not as a transfer, and ideally split out per source if you're tracking yield by account.
Keep the Full Picture in Your Books
Whichever structure you choose, the accounting question is the same: interest income from a treasury sweep is income, and it needs to show up on your books distinctly from principal movements between accounts — otherwise your P&L understates what your cash is actually doing for you, and your balance sheet gets murky about which balances live where. That's a common blind spot once cash starts flowing through three or four linked accounts instead of one.
Beancount.io's plain-text accounting approach makes this easy to get right: every sweep, every T-bill maturity, and every interest deposit is a transaction you can see in version-controlled, human-readable ledger files — no black-box dashboard hiding where a balance actually sits or how it got there. If you're managing cash across an operating account, a sweep network, and a treasury tier, tracking each as its own account in your chart of accounts gives you an audit trail your accountant (and your future self) can actually follow. Get started for free and see why finance-minded founders are moving their books to plain text.