The comparator is the whole test, and Congress and the Bureau did not choose the same one. Three federal provisions describe the same shape and measure it three different ways.
The Truth in Lending Act at 15 U.S.C. 1639(e) says no high-cost mortgage "may contain a scheduled payment that is more than twice as large as the average of earlier scheduled payments", and exempts a schedule adjusted to the consumer's seasonal or irregular income. Regulation Z, which implements the statute, states the same limitation at 12 CFR 1026.32(d)(1)(i) as "a payment schedule with a payment that is more than two times a regular periodic payment". An average of every earlier payment and a single regular periodic payment are the same number on a level-payment loan and different numbers on any loan whose payments change, so the two formulations part company on step-rate and adjustable schedules. A creditor tests against the regulation, and 12 CFR 1026.18(s)(5)(i) carries the identical wording for the disclosure duty. The same split runs through the qualified mortgage rules: Congress wrote the definition at 15 U.S.C. 1639c(b)(2)(A)(ii) around a payment "more than twice as large as the average of earlier scheduled payments", while the regulation implementing it sends the reader to 1026.18(s)(5)(i) instead.
The third comparator sits outside mortgage lending entirely. The Bureau's small-dollar rule at 12 CFR 1041.3(b)(2)(i) brings a loan into coverage where the consumer must repay substantially the entire balance in a single payment more than 45 days after consummation, or repay the loan "through at least one payment that is more than twice as large as any other payment(s)". There the balloon shape is not a prohibited term at all; it is one of the triggers that decides whether the rule applies to the loan in the first place.
Where a balloon payment comes from is arithmetic, and it is not a penalty. A lender calculates a level payment on one amortization period and writes the note for a shorter one. Every scheduled payment covers the interest accrued and reduces the balance exactly as it would on a fully amortizing loan, but the payments stop before the balance reaches zero, and what remains falls due in a single piece. The mechanics of how a level payment splits between interest and principal belong to amortization; the balloon is the remainder that split never reaches.
On mortgages the rules exclude the feature rather than outlaw it, and the distinction is load-bearing. Under 12 CFR 1026.43(e)(2)(i)(C) a qualified mortgage under the general definition must provide for regular periodic payments that do not "result in a balloon payment, as defined in § 1026.18(s)(5)(i), except as provided in paragraph (f)". That is a condition of qualified mortgage status, not a prohibition on lending, and paragraph (f) opens a narrow route for a small creditor operating predominantly in rural or underserved areas. A high-cost mortgage is closer to an outright bar: 12 CFR 1026.32(d)(1)(i) says such a loan may not include a payment schedule with a payment more than twice a regular periodic payment, with three exceptions at (d)(1)(ii) for closed-end credit (a schedule adjusted to seasonal or irregular income, a bridge loan of twelve months or less connected with acquiring or constructing the borrower's principal dwelling, and a loan meeting the small-creditor conditions at 1026.43(f) or (e)(6)) and a further exception at (d)(1)(iii) for the payment change an open-end plan makes when it moves from its draw period into its repayment period.
Outside those two categories the structure is ordinary and lightly regulated. Commercial real estate lending commonly uses the structure, with a five- or ten-year term laid over a twenty-five-year schedule. Bridge loans are balloons by construction, since the entire balance is meant to be retired by a sale. Seller-financed residential notes commonly end in one, and equipment and vehicle financing sometimes does. None of those loans carries the mortgage-disclosure duty at 1026.18(s), so on a business or seller-financed note the only place the balloon appears is the note itself.
What the rules do not do is guarantee an exit. No provision discussed here requires a lender to refinance, extend or modify the loan when the balance falls due, and a borrower planning to refinance is making a forecast about credit standards, interest rates and the value of the collateral on one specific future date. That risk is the subject of the balloon mortgage page, where it does the most damage.