Interest Cap¶
Protocol — instantiates Compounding Control
Limits compounding financial obligations so debt does not grow faster than repayment capacity or social legitimacy.
An Interest Cap fixes a ceiling on the rate at which a debt is allowed to multiply itself, set by rule before the loan is ever written. The defining move is that it governs the multiplier, not the balance: rather than forgiving what a borrower already owes or scheduling a repayment, it forbids the compounding engine — the effective interest rate, inclusive of fees and rollovers — from spinning fast enough to outrun the borrower's capacity to pay. Because interest on interest is the classic runaway trajectory (a small margin, repeated, becomes an inescapable balance), a cap placed on the rate changes every future cycle at once. The whole point is to make the ceiling bind on the all-in growth rate, so the loop cannot reconstitute the multiplier under a different name.
Example¶
A city is alarmed at storefront payday lenders whose two-week loans, rolled over month after month, leave borrowers owing several times what they first took. A single loan looks survivable; the sequence is the trap. The reform is an Interest Cap: no consumer credit product may carry a Military-APR-style all-in annualized rate above 36 percent — a threshold already used in federal lending to service members, chosen because above it a modest balance compounds beyond a typical household's ability to catch up. Crucially the cap is written against the effective rate: origination fees, rollover charges, and mandatory "insurance" all fold into the number, so a lender cannot advertise a legal headline rate while fees quietly restore the old multiplier. A licensed lender who wants to exceed the cap for a defined, higher-risk product must apply to the regulator, disclose loss data, and accept reporting obligations. The outcome is not that credit vanishes but that the fast-compounding, spiral-producing tier of it does.
How it works¶
- Define the compounding metric first. Everything hinges on measuring the effective rate — annualized, all-in — not the nominal one, so fees and rollovers cannot rebuild the multiplier outside the cap.
- Anchor the ceiling to a runaway threshold. The cap number is chosen relative to the point at which a debt outpaces plausible repayment or crosses a usury/legitimacy line, not picked for symmetry.
- Bind at origination, forward-only. The ceiling constrains the rate on new and renewed obligations; it does not itself pay down existing stock.
- Route overrides through exception governance. A named authority decides who may lend above the cap, on what evidence, for which product, and under what disclosure — so the cap is neither trivially bypassed nor blindly rigid.
Tuning parameters¶
- Cap level — where the ceiling sits relative to the runaway line. Lower protects borrowers more but rations credit harder; higher preserves access but lets more balances spiral.
- Metric breadth — whether the capped number is nominal interest or a fully-loaded effective APR. Broader closes fee-based evasion but is harder to compute and enforce.
- Product scope — which instruments the cap covers. Narrow scope is clean but invites migration into an uncovered product; broad scope catches evasion but sweeps in benign credit.
- Indexation — a fixed number versus a floating cap pegged to a benchmark rate. Floating stays proportionate as base rates move but is less legible to borrowers.
- Exception breadth — how easily a licensed lender may exceed the cap. Generous exceptions preserve high-risk lending but dilute the protection.
When it helps, and when it misleads¶
Its strength is prevention ex ante and cheap enforcement: one legible number, checkable at origination, that disarms the debt spiral before anyone is inside it. It also protects the socially legitimate face of lending — a rate the public will not read as predatory.
Its central failure mode is credit rationing: a cap set below what covers a lender's risk simply removes that credit rather than making it cheaper, and the marginal borrower is pushed toward unregulated or illegal lenders where no cap reaches.[n1] Because an Interest Cap carries no spillover monitor of its own, this displacement is exactly the harm it is blind to. The classic misuse is capping the headline rate while leaving fees, "membership" charges, and rollover penalties uncapped, so the effective multiplier is quietly reassembled. The guarding discipline is to cap the all-in effective rate and to watch, separately, where credit demand migrates when the ceiling binds.
How it implements the components¶
growth_cap— the ceiling on the effective interest rate is the growth cap, applied directly to the debt's multiplier.runaway_threshold— the cap is anchored to the rate above which balances outpace repayment or cross a usury/legitimacy line.compounding_metric— it forces measurement of the effective, all-in annualized rate rather than the nominal one.exception_governance— it defines who may lend above the cap, on what evidence, and under what disclosure.
It does not implement paydown_path for balances already accumulated — that staged reduction is Technical Debt Paydown Cadence's role — nor a spillover_monitor to track credit fleeing to unregulated lenders, which is Concentration Limit's contribution.
Related¶
- Instantiates: Compounding Control — an Interest Cap governs a financial compounding pathway by bounding its multiplier.
- Sibling mechanisms: Anti-Snowball Intervention · Epidemic Growth Control · Runaway Feedback Damping · Concentration Limit · Technical Debt Paydown Cadence · Decay Countermeasure Program · Progressive Friction
Editorial Notes¶
Form Classification¶
Form family: Rule, Policy & Commitment
Rationale: Interest Cap operates as a standing rule, threshold, contractual commitment, or policy constraint governing future conduct because it limits compounding financial obligations so debt does not grow faster than repayment capacity or social legitimacy
Independent corroboration: The frozen evidence defines Interest Cap as 'Limits compounding financial obligations so debt does not grow faster than repayment capacity or social legitimacy', so its operative form is Rule, Policy & Commitment.
Review outcome: Independent reviewer agreement; high confidence.
Origin Attribution¶
Primary origin: Law & Governance
Origin pattern: Convergent development
Present-day reach: Specialized
Rationale: An enforceable ceiling on interest is a usury-law and consumer-credit regulation instrument. Economics explains credit rationing and compounding effects, while public policy shapes affordability and evasion controls.
Related originating lineages:
- Economics & Finance — Compound-interest and borrower-capacity analysis materially define the economic harm and effective-rate measure.
- Public Administration & Policy — Regulatory enforcement and market-monitoring practice materially shape coverage, reporting, and anti-evasion rules.
Review resolution: An enforceable ceiling on interest is a usury-law and consumer-credit regulation instrument. Economics explains credit rationing and compounding effects, while public policy shapes affordability and evasion controls. The retained alternate domains identify documented formative or independently established origins, not downstream applicability alone. domain_reach=specialized because established use remains concentrated in a bounded professional context. The entry generalizes an established mechanism without inventing a new cross-domain composite.
Review outcome: Researched adjudication after independent review; high confidence.
Sources consulted:
- https://www.consumerfinance.gov/rules-policy/regulations/1026/47/ — CFPB official interpretation addressing statutory usury caps and maximum credit rates.
Notes¶
An Interest Cap acts only on the rate of future compounding; a borrower already deep in a spiral needs a paydown path or a reset in addition. Conflating the two — expecting a rate ceiling to shrink an existing balance — is a common way the tool is asked to do work it structurally cannot.
[n1] Credit rationing — the result, described in the Stiglitz–Weiss analysis of lending under imperfect information, in which lenders respond to a binding price ceiling by supplying less credit rather than lowering returns, so some borrowers are denied at any price. It is the standard caution against caps set below the level that covers risk. ↩