T-Bill Auto-Roll: TreasuryDirect vs Fidelity, Rule by Rule

There is a specific moment when a T-bill ladder starts to feel like it runs itself. You set it up, you watch the first few maturities land and roll into the next rung without you touching anything, and you start treating the whole structure the way you’d treat a savings account on autopilot. That feeling is mostly earned, but it hides two decisions that are still yours to make, and they are not the same decision on every platform. One is what happens to the money if the new bill costs more than the old one paid out. The other is what happens to the interest you already earned. Get comfortable with the autopilot before you know the answers, and you can end up with a ladder that quietly drains cash or one that stops compounding without ever sending you an alert.

The short answer: on TreasuryDirect, auto-reinvestment is a setting you choose after you already own the bill, and you can edit or cancel it right up until four business days before the next auction — but if the new bill’s price runs higher than what the old one paid you, TreasuryDirect will either pull the difference from your linked funds or cancel the roll outright. On Fidelity, enrolling in Auto Roll happens at the moment you place the original order, and while you can drop out later with no penalty, only the maturing principal gets rolled — the interest is dropped into your account as cash and never automatically reinvested on either platform.

TreasuryDirect: a decision you can still change

TreasuryDirect treats reinvestment as something you layer onto a security after you’ve bought it, and you can revisit that choice for as long as the reinvestment window stays open. The path is Manage Direct → Manage My Securities → Edit reinvestments, and from there you can turn a scheduled roll on, off, or swap which security it points to. Bills get the most flexibility in the system: TreasuryDirect states that “bills may be scheduled for multiple reinvestments, up to two years,” while “notes, bonds, and FRNs can only be scheduled for one reinvestment.” That asymmetry is worth sitting with if your ladder mixes maturities, because a 26-week bill you plan to roll for a year needs to be re-scheduled less often than you’d guess, but a note you’re rolling once will need your attention again once that single reinvestment executes.

The roll itself is narrow by design. TreasuryDirect requires that “the type of security must be the same,” so a 13-week bill only ever rolls into another 13-week bill — there’s no built-in way to auto-migrate from a 13-week rung into a 26-week rung just because rates moved. If you want to reshape the ladder, that has to happen by hand.

The part that catches people off guard is the deadline. TreasuryDirect “closes the option to reinvest four business days before the relevant auction,” and the flip side of that is your leverage: “you can change or cancel a reinvestment, as long as it’s more than four business days before the new auction.” Four business days sounds generous until you realize it’s counted against the auction date, not the maturity date, and those two dates aren’t identical. If you’re watching a Fed decision or a jobs report and thinking about whether to keep a rung rolling into short bills or redirect it, that four-day window is the actual clock you’re working against, not the calendar reminder most people set for the maturity date itself.

Then there’s the money mechanic that makes TreasuryDirect genuinely different from a brokerage sweep. Because reinvestment happens at auction, the new bill’s price isn’t fixed when you schedule the roll — it’s set by that auction’s yield. TreasuryDirect is explicit that “you may owe more for the new security than you are getting for your maturing security,” and the fix is on you: “make sure funds are available in your bank account or C of I to cover the difference before the issue date.” Skip that step and the system doesn’t extend you credit. “If funds are not available to pay the difference, we will cancel the reinvestment and deposit the proceeds of the maturing security into your bank account or C of I.” In practice, that means a ladder can un-ladder itself silently the moment yields shift enough to make the new bill pricier and your linked account is a little light. One more boundary worth knowing: TIPS aren’t part of any of this. You can reinvest bills, notes, bonds, and FRNs on TreasuryDirect, but not TIPS — if you’re holding inflation-protected securities, rolling them is a manual rebuy every time, and it’s worth reading up on how TIPS phantom income gets taxed before you decide whether TreasuryDirect is even the right home for them. If your plan involves buying more bills through TreasuryDirect in the first place, the mechanics of how to buy through TreasuryDirect are the logical starting point.

Fidelity: the checkbox that ships with the order

Fidelity’s Auto Roll program sits at a different point in the timeline entirely. Instead of a setting you add after the fact, it’s built into the purchase itself: you enroll by choosing to “select Yes on the Auto Roll option displayed on the order entry screen,” after agreeing to the Auto Roll Service Agreement and the accompanying alerts. There’s no separate trip to a settings page after the fact — the decision is made, or not made, in the same click that buys the bill.

Eligibility is narrower than “any Treasury you own.” Fidelity limits Auto Roll to “Treasury auction securities, new-issue CDs with a term to maturity of 5 years or less,” while excluding TIPS, CMBs, and anything purchased on the secondary market rather than at a new issue. There’s also a ceiling: enrollment tops out at $250,000 per purchase, which matters if you’re laddering at a scale where a single rung could bump against that limit.

The mechanic that most resembles a trap, if you don’t read past the headline feature, is what actually gets rolled. Fidelity states plainly that “only the maturing principal will be applied to any subsequent Auto Roll position purchase” and that “no interest payments from these positions will be included in any Auto Roll position purchase.” The interest lands in your account as ordinary cash, available to spend, hold, or manually reinvest, but it will not compound into the next rung on its own. Run a ladder on Auto Roll for a year without ever sweeping that cash back in, and the ladder itself stays exactly the size it started at while a slowly growing pile of un-invested interest sits next to it. The one thing Fidelity does make easy is opting back out: “you have the ability to withdraw from the service at any time with no penalties,” so if a particular rung needs to become cash instead of rolling again, canceling that position’s participation is straightforward. One clarification worth making explicitly, because Fidelity’s own materials can blur it: the rule about a “settlement date within twelve calendar days following stated maturity date” applies to the CD side of Auto Roll, not to Treasuries. A rolled Treasury moves into the next scheduled auction; that twelve-day settlement language isn’t the mechanism governing your T-bill rungs, and treating it as if it were is a good way to misjudge how quickly a roll actually executes.

Which one actually fits your ladder

Laid side by side, the two programs aren’t really competing on the same axis. TreasuryDirect gives you a reversible decision with a real deadline attached — you can watch rates, watch the calendar, and change your mind up until four business days before the next auction, but you take on the job of keeping enough cash on hand to cover a pricier reinvestment, or the roll quietly cancels itself. Fidelity gives you a decision made once, at purchase, that then runs largely unattended, but principal-only rolling means the ladder itself never grows unless you manually redirect the interest it throws off. Neither platform compounds the full return for you; TreasuryDirect’s risk is that a funding gap breaks a roll, and Fidelity’s risk is that idle interest cash quietly caps how much your ladder can grow.

If you’re the type who checks yields before FOMC meetings and might want to redirect a rung on short notice, TreasuryDirect’s editable window rewards that attention. If you’d rather set it up once and only intervene to sweep interest back in every few months, Fidelity’s order-time enrollment removes a recurring task at the cost of that flexibility. Other brokers run similar auto-roll programs with their own eligibility rules and cutoffs, so the general shape — enroll once, principal-only, cancel anytime — tends to repeat even where the specific numbers differ. And if life intervenes and you need to move a TreasuryDirect holding into a brokerage entirely, know going in that a transfer via FS Form 5511 cancels any reinvestment instructions attached to that security the moment it moves — the roll doesn’t follow the bill to its new home. If the real question isn’t rolling at all but getting cash out before maturity, that’s a different problem with its own rules, covered in selling a T-bill before maturity on TreasuryDirect. For the wider context of where T-bills sit against other cash tools, the savings hub is the place to start.

Sources

• TreasuryDirect, “Reinvesting a Treasury Marketable Security”: https://www.treasurydirect.gov/marketable-securities/reinvesting-a-marketable-security/
• Fidelity, “Auto Roll Program”: https://www.fidelity.com/fixed-income-bonds/fixed-income-tools-services/auto-roll-program