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Summary

Add parameters documenting student loan interest rate rules:

  • Plan 1: Lower of RPI or base rate + 1%
  • Plan 2: Income-contingent (RPI to RPI+3% based on income thresholds)
    • Lower threshold: Same as repayment threshold (£28,470 for 2025)
    • Upper threshold: £51,245 for 2025
    • Below lower threshold: RPI only
    • Above upper threshold: RPI + 3%
    • Between thresholds: Tapered rate
  • Plan 4: Same as Plan 1
  • Plan 5: RPI only (no income-based component)
  • Postgraduate: RPI + 3%

Why add these?

While interest accrual isn't currently modelled in the microsimulation (it requires tracking loan balances over time), these parameters document the policy rules for:

  1. Reference and documentation
  2. Potential future use in lifetime models
  3. Completeness of the student loan policy representation

Test plan

  • Parameters load correctly (no syntax errors)
  • Values match GOV.UK published rates

References

Fixes #1417

🤖 Generated with Claude Code

@MaxGhenis MaxGhenis force-pushed the add-student-loan-interest-rates branch 2 times, most recently from e2c97a8 to 3b1aa99 Compare November 30, 2025 00:48
Add parameters documenting student loan interest rate rules:
- Plan 1: Lower of RPI or base rate + 1%
- Plan 2: Income-contingent (RPI to RPI+3% based on income thresholds)
- Plan 4: Same as Plan 1
- Plan 5: RPI only (no income-based component)
- Postgraduate: RPI + 3%

Add student_loan_interest_rate variable that calculates the applicable
rate based on plan type and income, with Plan 2 tapering between the
lower and upper income thresholds.

Fixes #1417

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
@MaxGhenis MaxGhenis force-pushed the add-student-loan-interest-rates branch from 3b1aa99 to fd36a13 Compare November 30, 2025 00:51
@MaxGhenis
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Superseded by #1420 (merged) and #1423. The approach in those PRs uses separate variable files for each plan's interest rate and calculates from parameters (RPI + margin) rather than hardcoding values.

@MaxGhenis MaxGhenis closed this Dec 1, 2025
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Add student loan interest rate parameters

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