Best Fidelity Core Position: SPAXX vs. FZFXX vs. FCASH vs. FDIC Sweep

Rates here are snapshots: fund yields and the sweep APY as of August 31, 2026, and Fidelity’s posted FCASH rate dated December 12, 2025. The mechanics of how the core position works change far more slowly than the rates do.

Every Fidelity brokerage account has a core position, whether or not you have ever thought about it. Fidelity establishes one automatically when the account is opened, and from then on it is the account’s cash wallet: deposits land in it, stock and fund purchases draw from it, sale proceeds sweep back into it, and checks, debit card charges, bill pay, and transfers all pull from it with no action on your part.¹ Because every uninvested dollar sits there by default, the core position quietly sets the yield on more of your money than almost any deliberate choice you make in the account.

The choice matters because the options pay very different rates. At the August 31, 2026 snapshot, the money market options paid 3.33% to 3.35% while the FDIC sweep paid 1.84% APY and FCASH paid 1.82% (per Fidelity’s December 2025 posting), a spread of roughly 1.5% a year on whatever cash the account holds.²³ On $25,000 of average uninvested cash, sitting in the wrong core costs about $375 a year at those rates.

Your options depend on the account type

There is no universal menu. Fidelity offers a different core lineup per account type, and additional options can exist for some accounts, so check your own account’s list before assuming.¹⁸

The candidates, one verdict each

SPAXX: the right default for most accounts

The Fidelity Government Money Market Fund yielded 3.33% (7-day yield, August 31, 2026), holds government and agency paper plus government-collateralized repurchase agreements, and targets a stable $1.00 share price.² It combines the highest broadly available core yield with full transaction automation, which is why Fidelity defaults most accounts into it. Its weak spot is state tax: only 50.90% of its 2025 income was U.S. government source, and it failed the minimum-investment test California, Connecticut, and New York impose, so residents of those states get no state exemption on 2025 SPAXX dividends at all.⁶

FZFXX: nearly a coin flip with SPAXX

The Fidelity Treasury Money Market Fund yielded 3.35% at the same snapshot, two basis points above SPAXX.² Its 2025 government-source share was higher, 61.52% versus 50.90%, but it failed the same CA/CT/NY test, so the three states where a Treasury fund’s tax edge would matter most are exactly the states where it evaporates.⁶ Elsewhere, the extra exemption is worth about $18 a year per $100,000 at a 5% state rate using the 2025 percentages and August 2026 yield. Pick whichever of the two you like; the difference is small enough that it should not consume any of your attention.

FDIC sweep: for when deposit insurance is the requirement

The FDIC-Insured Deposit Sweep places your cash in interest-bearing accounts at a rotation of program banks, keeping each bank’s slice at $245,000 so accrued interest stays inside the $250,000 FDIC limit; Fidelity states that with available bank capacity, up to $4 million of uninvested cash across eligible accounts can be FDIC covered.⁴ The price of that coverage was roughly 1.5% of yield at the August 2026 snapshot (1.84% APY versus 3.33%).³ Two fine-print items: deposits you already hold at a program bank count against the same $250,000 limit, and Fidelity puts the monitoring burden on you; and overflow cash that exceeds bank capacity lands in a money market fund (FZSXX) that is not FDIC insured.⁵ Choose the sweep when explicit deposit insurance is non-negotiable, and know what it costs per year; otherwise the money market options pay more for risk that is different in kind but similarly remote.

FCASH: the one to move away from

FCASH is a free credit balance, an obligation of the broker payable on demand rather than a fund you own. Fidelity’s posted rate was 1.82% as of December 12, 2025.¹ It has no FDIC insurance and no underlying portfolio, and at these rates it pays about 1.5% less than SPAXX in the same account. If a taxable account is sitting in FCASH, changing the core to SPAXX takes a minute online and is the rare free lunch in this guide. (Accounts are not universally defaulted into FCASH; many were simply opened before the current defaults or chosen without attention.)

Beyond the core: the two-list strategy

The core menu is short, but the core is only the first draw. Fidelity settles debits in a documented order: intraday free credit, then the core position, then any other stable-value Fidelity money market fund held in the account.⁹ That last step means you can keep a modest balance in the core and separately buy a better-taxed fund, and Fidelity will automatically liquidate it to cover checks or purchases when the core runs dry.

The two purchases worth knowing about, with 2025 tax-document figures:

• FDLXX (Fidelity Treasury Only Money Market Fund): 3.39% 7-day yield on August 31, 2026, 98.67% government-source income for 2025, and it passed the CA/CT/NY test. It is absent from Fidelity’s core lists, so it takes one manual buy, after which the auto-liquidation above covers you.⁶
• SGOV (iShares 0-3 Month Treasury Bond ETF): higher still after tax in most brackets, but it is an ETF, so sales settle T+1 and it is outside the automatic draw order. Our SPAXX vs. SGOV guide prices that trade-off in dollars.

Compare your actual options

Pick your account type and the picker limits the comparison to the core options generally available there, then ranks them after tax at your rates.

FDIC and SIPC protect against different failures

The insurance question causes more confusion than any other part of this decision, and the two acronyms are answers to different risks:

• FDIC insures bank deposits against the bank failing, $250,000 per depositor, per bank, per ownership category. Within the core menu, only the deposit sweep gets it.
• SIPC steps in if the brokerage fails with customer assets missing, up to $500,000 including $250,000 for cash. Money market fund shares count as securities under SIPC, and SIPC never covers a decline in the value of an investment.⁷

A government money market fund is therefore not “uninsured cash”: it is a security you own, backed by a portfolio of government-related paper, with SIPC behind the custody of it. What it lacks is a federal guarantee of the $1.00 price. The historical record for government money market funds is strong, and it is still a different promise than deposit insurance.

How to change it

From your Positions view, select the core position row and choose “Change core position,” or call Fidelity. Only one fund can be the core at a time; changing it does not sell anything, it just redirects where uninvested cash lives from then on.¹

Key takeaways

• The core position is a default worth checking. It sets the yield on every uninvested dollar, and the options spread about 1.5% a year at August 2026 rates.
• SPAXX is the sensible default in every account type that offers it: top-of-menu yield with full automation.
• FZFXX is a rounding-error upgrade at best. Two basis points of yield and a state-tax edge worth roughly $18 a year per $100,000 at a 5% state rate (2025 percentages), and nothing at all in CA, CT, or NY, where it failed the 2025 minimum.
• The FDIC sweep is a deliberate insurance purchase. About 1.5% of yield bought explicit deposit coverage at the August 2026 snapshot; buy it when that assurance is the requirement.
• Move out of FCASH. Lowest rate on the menu, no insurance, no fund. Changing the core takes a minute.
• High-tax-state investors should look past the core menu. FDLXX (separately purchased, auto-liquidated when needed) or SGOV carry the state-tax exemption that SPAXX and FZFXX failed to deliver for 2025 in CA/CT/NY.

How Summitward helps

Frequently asked questions

What is a core position at Fidelity?

The account’s holding place for uninvested cash. Fidelity creates it automatically at account opening and uses it to process every cash transaction: deposits, purchases, sale proceeds, withdrawals, checks, and debit activity. You can have only one core position per account, though you can hold other money market funds alongside it.

Is SPAXX FDIC insured?

No. It is a money market mutual fund, protected as a security by SIPC if the broker fails, with a portfolio of government-related holdings. The FDIC-insured core option is the deposit sweep, which paid 1.84% APY versus SPAXX’s 3.33% as of August 31, 2026.

Why can’t I pick FZFXX in my IRA?

Fidelity’s core menu differs by account type. Retirement accounts generally offer SPAXX or the FDIC sweep; FZFXX and FCASH appear on the taxable brokerage menu. Since IRA income is not state-taxed as it accrues, FZFXX’s Treasury angle would buy nothing there anyway.

Why is FDLXX missing from the core list?

Fidelity’s published core lineups simply do not include it. Buy it as a regular position; Fidelity’s settlement order will automatically redeem it to cover debits once your core is exhausted, which in practice gives you most of the convenience of a core with FDLXX’s better state-tax profile.

How much FDIC coverage does the sweep actually provide?

Fidelity spreads balances across program banks at $245,000 apiece and cites up to $4 million of coverage across eligible accounts when bank capacity allows. Money you separately hold at one of the program banks counts against the same $250,000 per-bank limit, and Fidelity states that monitoring the overlap is your responsibility. Cash beyond available capacity overflows into a money market fund that is not FDIC insured.

Does changing my core position trigger taxes?

No sale of your investments occurs, and money market funds transact at a stable $1.00, so switching cores does not create gains. The dividends each core pays are taxable in a taxable account, as they were before the switch.

Related guides

• SPAXX vs. SGOV: Which Is Better for Cash at Fidelity?: whether reserve cash should leave the core entirely.
• Where to Park Your Cash: the full layered framework beyond any one brokerage.
• Fidelity ZERO Funds: how Fidelity prices the rest of its lineup.
• Emergency Fund Sizing: how much should be sitting in cash at all.

Sources

1. Fidelity, “Trading FAQs: About Your Trading Account” (core mechanics, per-account-type core lists, FCASH description and rate, how to change the core). fidelity.com
2. Fidelity Institutional, “Fidelity Money Market Funds: Month-End Yields,” as of August 31, 2026 (SPAXX 3.33%, FZFXX 3.35%, FDLXX 3.39%). institutional.fidelity.com
3. Fidelity, FDIC-Insured Deposit Sweep interest rates (1.82% rate / 1.84% APY, August 31, 2026; FZSXX overflow disclosure). digital.fidelity.com
4. Fidelity, “Safeguarding Your Accounts” ($245,000 per program bank; up to $4 million of FDIC eligibility with available capacity). fidelity.com
5. Fidelity, FDIC-Insured Deposit Sweep Program Disclosure (maximum deposit limit mechanics, customer aggregation and monitoring responsibility, Money Market Overflow). fidelity.com (PDF)
6. Fidelity, “2025 Percentage of Income from U.S. Government Securities” (SPAXX 50.90%, FZFXX 61.52%, FDLXX 98.67%, with the CA/CT/NY minimum-investment footnote). fidelity.com (PDF)
7. SIPC, “What SIPC Protects.” sipc.org
8. Fidelity, Cash Management Account FAQs (CMA core options; sweep mechanics example). fidelity.com
9. Fidelity Account Customer Agreement (order of sources used to settle debits, including redemption of non-core Fidelity money market funds). fidelity.com (PDF)

Author disclosure

Educational content, not investment or tax advice. Rates are dated snapshots and the government-source percentages are 2025 tax-year figures that reset annually; verify both against the primary sources above before acting. Core availability can vary by account, so treat Fidelity’s own menu for your account as authoritative. Summitward has no affiliation with Fidelity.