Hypothetical worked example and primary educational references; not observed market data.
A tier table does not explain its application by itself
A deposit can use different rates for different balance levels, but there are at least two important ways to apply them. Under a marginal structure, each rate applies only to the money within its band. Under a whole-balance structure, the applicable tier determines a rate for the entire balance. CFPB's APY appendix distinguishes these methods in the US disclosure context. Reading only the largest percentage in a tier table can therefore misstate the earnings on an actual balance. Before calculating interest, identify which units receive which rate. The difference is structural, so no amount of decimal precision can correct a calculation based on the wrong interpretation of the bands.
Supporting references: 1. CFPB: Regulation DD, Appendix A
Marginal tiers require separate currency calculations
In a marginal structure, multiply the amount in each band by that band's rate, then add the interest amounts. Divide the total interest by the total balance to obtain a simple one-year blended yield under the stated assumptions. The worked example keeps USD 10,000 in place for one year. The first USD 4,000 earns an invented four percent, while the remaining 6000 earns two percent. The table excludes within-year compounding to isolate the allocation. Applying four percent to the entire balance would overstate interest because the higher rate covers only the first band. Applying two percent to the entire balance would omit the higher-rate band's contribution. Both mistakes arise from failing to assign money to bands before computing earnings.
Hypothetical worked example
Two tier structures at the same balance
Model setup
Read these assumptions before comparing the scenarios.
- All monetary amounts in this example are hypothetical U.S. dollars (USD), not current prices, quoted account terms or observed market data. Percentages, counts, time periods and index levels retain their stated units.
- Balance is USD 10,000 for one year; no compounding within the year.
- First USD 4,000 earns 4%, remaining 6000 earns 2% under marginal tiers.
- Whole-balance alternative pays 2% on all USD 10,000; terms are invented.
Calculated result (percent blended one-year yield)
- Marginal tiers2.80
- Whole-balance 2% tier2.00
Shared zero-based scale; negative values extend to the left.
- Lowest displayed value
- 2.00
- Highest displayed value
- 2.80
Hypothetical cases from the table below, in the stated units. Not market observations, a forecast or a recommended choice. Read the scenario assumptions before comparing.
| Hypothetical scenario | Calculated result (percent blended one-year yield) |
|---|---|
| Marginal tiers | 2.80 |
| Whole-balance 2% tier | 2.00 |
Calculation details
- Marginal tiers
- 2.80 percent blended one-year yield
((((4000 * 0.040000000000000001) + (6000 * 0.02)) / 10000) * 100) - Whole-balance 2% tier
- 2.00 percent blended one-year yield
(((10000 * 0.02) / 10000) * 100)
Whole-balance tiers change the entire base
For a whole-balance structure, determine the applicable tier from the qualifying balance and apply its rate to all money covered by the rule. The example's comparison row assumes two percent on the entire USD 10,000 balance. A threshold crossing can therefore change earnings on existing units, not just on an additional deposit. That can create an abrupt change in the modeled result. Whether such a change occurs in a real account depends on the actual structure and balance method. Do not infer it from the word tiered alone. The contrast in the table is a mathematical explanation of two possibilities, not a statement that institutions use these exact bands or that one arrangement is universally better.
The next unit can have a different yield from the average
Under marginal tiers, the average yield on the current balance and the yield on the next added unit can differ. The average includes money already earning in earlier bands, while the additional unit may receive only the current marginal rate. This is useful when evaluating a new contribution. A headline describing the blended yield does not necessarily describe the incremental earnings from adding more money. Under a whole-balance structure, an additional deposit can also change the rate on all existing units if it crosses a boundary. A comparison should therefore state whether it concerns the current balance, an additional amount, or the total after a threshold crossing. Those questions require different calculations even within the same account.
Use the actual balance path and disclosures
US account-disclosure rules address tiered rates and corresponding yields. For a practical estimate, obtain the account's band definition, qualifying balance method, compounding schedule, and potential changes. A fixed opening balance may not remain in one tier after withdrawals, deposits, or fees. The table assumes a constant balance and simple annual earnings, so its blended percentages are teaching measures rather than substitutes for a legally disclosed APY. Keep the allocation table visible when explaining the result; it shows why the average emerges instead of presenting an unexplained rate. This approach supports careful deposit comparison while avoiding the assumption that the most prominent percentage applies to every unit or to the next unit the saver contributes.
Supporting references: 2. CFPB: Regulation DD account disclosures
Test another situationThe next deposit may earn less than the existing average
A separate hypothetical case. Its inputs differ from the main worked example above.
The next deposit may earn less than the existing average
Assume hypothetical marginal tiers pay simple annual interest of 5% on the first USD 2,000 and 1% above that amount, with money unchanged for a year. USD 3,000 earns USD 110. Adding USD 1,000 at the start increases annual interest to USD 120, so the added principal earns only USD 10. The highest advertised band does not describe the marginal deposit. These are invented terms without compounding or charges. The trade-off is allocating new money to a lower-paying band while preserving whatever access the account supplies, rather than assuming the existing blended outcome applies equally to every added dollar.
Inspect whether the threshold reprices old money
CFPB's APY appendix distinguishes tier structures. A useful implementation test compares balances just below and just above a threshold while tracing which units receive a changed rate. Under marginal tiers, an additional unit enters its band without repricing prior units. Under whole-balance tiers, crossing the threshold can alter earnings on the full qualifying balance. Do not infer either rule from the tier table's formatting. A statement comparison also needs the actual qualifying balance method and transaction dates. If a withdrawal moves money across bands, recompute the affected exposure rather than applying the opening blended yield to the entire period's changing balance.
Supporting references: 1. CFPB: Regulation DD, Appendix A
Check this case’s calculations
- Interest on initial tiered balance
- 110.00 USD
((2000 * 0.050000000000000003) + (1000 * 0.01)) - Interest after extra deposit
- 120.00 USD
((2000 * 0.050000000000000003) + (2000 * 0.01)) - Interest earned by added principal
- 10.00 USD
(120 - 110)
Limits of this additional case
- The tier example uses simple annual interest and marginal bands; it is not a disclosed APY calculation.
Limits of this analysis
- Actual APY tier calculations can include compounding and additional rules.
- Balances can move between tiers during the year.
- Neither hypothetical structure represents a current deposit offer.
Sources and scope
- CFPB: Regulation DD, Appendix A
APY annualizes interest relative to principal and term under specified assumptions.
Scope: US covered deposit disclosures; not a universal account formula.. Reference accessed 2026-10-06.
- CFPB: Regulation DD account disclosures
Covered account disclosures address rates, balance methods, fees, and time-account conditions.
Scope: US Regulation DD; educational discussion does not establish individual legal rights.. Reference accessed 2026-10-06.
Illustrative calculations are not forecasts or personal recommendations. Editorial standards
