Figure Descriptions

Figure 1: Promotional and Normal APYs in the Six-Bank Calibration

A grouped bar chart comparing the promotional APY (blue bars) and normal/post-promotion APY (magenta bars) across six U.S. digital banks: SoFi, Ally, Marcus, Discover, Varo, and CIT Bank. The figure illustrates the yield spread that creates the arbitrage opportunity, with promotional rates ranging from 4.35% to 5.20% and normal rates from 3.00% to 3.60%. Varo offers the highest promotional rate (5.20%) but the lowest normal rate (3.00%), while CIT Bank shows the smallest promotional spread.

Figure 2: Signup Bonuses and Promotional Deposit Caps in the Six-Bank Calibration

A dual-axis chart displaying signup bonuses as blue bars (left axis, in dollars) and deposit caps as a black line with markers (right axis, in thousands of dollars). SoFi offers the highest bonus ($300) with a $50,000 cap, while CIT Bank has the highest cap ($250,000) with a $175 bonus. The figure highlights the inverse relationship between bonus size and deposit capacity across institutions.

Figure 3: Computed Wealth Trajectories over 36 Months

A line plot showing wealth accumulation paths under five benchmark strategies starting from $50,000 initial capital over a 36-month horizon. Strategies include: Static HYSA (blue), Calendar Rotation (magenta), Calendar + Bonus (teal), Bellman Proxy (purple), and Bonus-Aware Bellman Proxy (green). The Bonus-Aware Bellman Proxy achieves the highest terminal wealth (~$56,273), while the static benchmark reaches ~$54,389, demonstrating the value of eligibility-aware optimization.

Figure 4: Reported Monte Carlo Premiums by Strategy

A bar chart displaying the promotional arbitrage premium (percentage gain over static HYSA) across five strategies based on 50,000-path Monte Carlo simulations. The regime-switching optimal strategy yields the highest premium at 14.65%, followed by Promo + Bonus at 12.06%, Optimal Deterministic at 7.59%, and Simple Calendar Rotation at 4.48%. Error bars reflect simulation standard errors.

Figure 5: Sensitivity of the Promotional Arbitrage Premium to Key Parameters

A tornado-style sensitivity diagram showing how the arbitrage premium (%) varies under low, base, and high scenarios for six parameters: tax rate, bonus size, switching cost, promotional volatility, requalification period, and inflation. The premium is most sensitive to bonus size (range: ~11% to ~29%) and requalification length, and least sensitive to inflation. Base-case premium is anchored at approximately 20%.

Figure 6: Eligibility-State Transitions

A state-transition diagram illustrating the three eligibility states for each bank: Ineligible/Waiting (0), Eligible for Promotion (1), and Active Promotion (2). Arrows indicate transitions triggered by account opening/switching, promotional expiration, and requalification period lapse. This figure visualizes the mode-dependent feasibility structure that distinguishes the model from standard switching problems.

Data Description for Zenodo Repository

The replication dataset (data_V3.xlsx) contains seven worksheets supporting the numerical calibration, simulation, and sensitivity analysis reported in the manuscript. All monetary values are in U.S. dollars unless otherwise specified.

Data Sources

Federal Reserve Economic Data (FRED), Bankrate, Marcus by Goldman Sachs, FDIC Quarterly Banking Profile, IRS Publication 17, NACHA Operating Rules, Doctor of Credit. Retrieval date: 2026-05-26.

Usage

These data support replication of the dynamic programming calibration, Monte Carlo validation, bootstrap inference, and sensitivity analyses reported in the manuscript. The six-bank subset (Bank_Promo_Rates) is the primary calibration input; the offer-level summary provides external validity for parameter ranges.