# Student Finance Calculator

> A comprehensive UK student loan repayment calculator featuring Plan 1, 2, 4, 5 and Postgraduate loan projections. Built with Next.js 15, TypeScript, and a server-side calculation engine. Provides yearly breakdowns, overpayment optimization, career scenario modelling, and educational guides. Updated for 2025/26 tax year.

Student Finance Calculator is a Next.js (App Router) TypeScript application that helps UK students and graduates understand their student loan repayments. The site offers:

- **Calculators:** Interactive tools for each loan plan (Plan 1, 2, 4, 5, Postgraduate) plus advanced scenarios (overpayments, combined loans, salary impact, total cost analysis)
- **Guides:** Comprehensive articles covering repayment strategies, tax implications, life events (maternity, moving abroad, self-employment), and financial planning
- **Comparisons:** Analysis of different loan plans and salary scenarios
- **API:** Public calculation endpoint for loan repayment projections
- **Plan Finder:** Interactive tool to determine which loan plan applies to a user

The calculation engine uses historical interest rate data and current UK government thresholds to provide accurate projections. All business logic is server-side (marked with 'server-only') to protect sensitive algorithms.

**Key Technical Features:**
- Server Components by default for optimal performance
- Zod-validated API with rate limiting and CORS protection
- Unit-tested calculation logic (Jest) and E2E tested user flows (Playwright)
- Static plan data in `src/lib/data/plan-data.ts` as single source of truth
- Recharts for data visualization
- Privacy-focused (no user data stored, client-side only calculations)

## Technical Documentation

- [Architecture Overview](https://studentfinancecalculator.co.uk/docs/architecture.md): Complete technical architecture, project structure, core patterns, testing strategy, and deployment details
- [API Reference](https://studentfinancecalculator.co.uk/docs/api-reference.md): Full API documentation for `/api/calculate` endpoint including request/response schemas, parameters, validation, error handling, and usage examples
- [Plan Data Reference](https://studentfinancecalculator.co.uk/docs/plan-data-reference.md): Authoritative data for all UK student loan plans (thresholds, interest rates, write-off periods) with historical rate data

## Core Calculators

- [Plan 1 Calculator](https://studentfinancecalculator.co.uk/calculators/plan-1): Pre-2012 England/Wales or Scottish undergraduate loans. £26,065 threshold, 9% repayment, 25-year write-off
- [Plan 2 Calculator](https://studentfinancecalculator.co.uk/calculators/plan-2): 2012-2023 England/Wales undergraduate loans. £28,470 threshold, RPI-linked interest, 30-year write-off. Most common plan type
- [Plan 4 Calculator](https://studentfinancecalculator.co.uk/calculators/plan-4): Post-1998 Scottish loans. £32,745 threshold, 9% repayment, 30-year write-off
- [Plan 5 Calculator](https://studentfinancecalculator.co.uk/calculators/plan-5): 2023+ England undergraduate loans. £25,000 threshold, RPI-only interest, 40-year write-off
- [Postgraduate Calculator](https://studentfinancecalculator.co.uk/calculators/postgraduate): Masters and PhD loans. £21,000 threshold, 6% repayment, 30-year write-off. Can combine with undergraduate loans (15% total deduction)

## Advanced Calculators

- [Overpayment Calculator](https://studentfinancecalculator.co.uk/calculators/overpayment): Model voluntary overpayments and calculate optimal monthly amounts to minimise total repayment or achieve early payoff
- [Combined Loan Calculator](https://studentfinancecalculator.co.uk/calculators/combined): Project repayments for multiple loan types simultaneously (e.g., undergraduate + postgraduate)
- [Total Cost Calculator](https://studentfinancecalculator.co.uk/calculators/total-cost): Comprehensive lifetime analysis including total paid, interest charges, write-off amounts, and effective interest rates
- [Salary Impact Calculator](https://studentfinancecalculator.co.uk/calculators/salary-impact): See how salary changes, raises, bonuses, and career progression affect monthly repayments and loan duration

## Essential Guides

- [How Student Loans Work](https://studentfinancecalculator.co.uk/guides/how-student-loans-work): Complete beginner's guide to UK student loan system, plan types, and repayment mechanics
- [Repayment Thresholds Explained](https://studentfinancecalculator.co.uk/guides/repayment-thresholds): When repayments begin, how thresholds work, and annual threshold changes
- [Interest Rates Explained](https://studentfinancecalculator.co.uk/guides/interest-rates-explained): How interest is calculated for each plan, RPI-linking, and compound interest effects
- [Student Loan Tax Codes](https://studentfinancecalculator.co.uk/guides/student-loan-tax-codes): Understanding payslips, Plan 1/2/4/5 tax codes, and PAYE deductions
- [Student Finance for Applicants](https://studentfinancecalculator.co.uk/guides/student-finance-for-applicants): Reality check and planning guide for prospective students considering student loans

## Strategic Planning Guides

- [Should I Overpay My Student Loan?](https://studentfinancecalculator.co.uk/guides/is-overpaying-worth-it): When overpaying makes financial sense (high earners, short payoff timeline) vs when to invest elsewhere
- [Pension vs Overpayments](https://studentfinancecalculator.co.uk/guides/pension-vs-overpayments): Tax efficiency comparison. Why pension contributions often beat overpayments for reducing effective repayment rate
- [High Earners with Postgrad & Plan 2](https://studentfinancecalculator.co.uk/guides/high-earners-postgrad-plan-2): Strategy for managing combined undergraduate + postgraduate debt with high income
- [Salary Sacrifice & Student Loans](https://studentfinancecalculator.co.uk/guides/salary-sacrifice-student-loans): Using salary sacrifice (pension, cycle-to-work, childcare vouchers) to legally reduce student loan repayments
- [Multiple Jobs & Student Loans](https://studentfinancecalculator.co.uk/guides/multiple-jobs-student-loans): How PAYE handles multiple employers, avoiding overpayment, and self-assessment implications

## Life Events & Special Circumstances

- [Maternity Pay & Student Loans](https://studentfinancecalculator.co.uk/guides/maternity-pay-student-loans): Impact of reduced income during maternity/paternity leave on repayments and loan balance growth
- [Moving Abroad with Student Loans](https://studentfinancecalculator.co.uk/guides/moving-abroad-student-loans): Obligations for expats, overseas repayment thresholds, SLC contact requirements, and enforcement
- [Self-Employment & Student Loans](https://studentfinancecalculator.co.uk/guides/self-employment-student-loans): Freelancer and contractor guide. Self-assessment, payment on account, and managing irregular income
- [Student Loans & Mortgages](https://studentfinancecalculator.co.uk/guides/student-loans-mortgages): How student loan repayments affect mortgage affordability calculations and debt-to-income ratios

## Plan Explanations

- [Plan 1 Explained](https://studentfinancecalculator.co.uk/plans/plan-1): Pre-2012 England/Wales & Scotland loans. Details on thresholds, interest calculation, write-off conditions, and who has this plan
- [Plan 2 Explained](https://studentfinancecalculator.co.uk/plans/plan-2): 2012-2023 England/Wales loans. Variable interest rates, threshold details, 30-year write-off, and repayment strategy
- [Plan 4 Explained](https://studentfinancecalculator.co.uk/plans/plan-4): Scottish post-1998 loans. Threshold rules, interest rates, 30-year write-off, and regional differences
- [Plan 5 Explained](https://studentfinancecalculator.co.uk/plans/plan-5): 2023+ England loans. New threshold rules, RPI-only interest, 40-year write-off, and policy changes
- [Postgraduate Loans Explained](https://studentfinancecalculator.co.uk/plans/postgraduate): Masters and doctoral loan details. Separate repayment structure, combining with undergraduate loans

## Plan Comparisons

- [Plan 1 vs Plan 2](https://studentfinancecalculator.co.uk/compare/plan-1-vs-plan-2): Threshold, interest, and write-off comparison. Plan 1: lower threshold, lower interest. Plan 2: higher threshold, RPI-linked interest
- [Plan 2 vs Plan 5](https://studentfinancecalculator.co.uk/compare/plan-2-vs-plan-5): Modern England plans. Plan 5: lower threshold (£25k vs £28.5k), RPI-only interest, 40-year write-off
- [Plan 4 vs Plan 5](https://studentfinancecalculator.co.uk/compare/plan-4-vs-plan-5): Scottish vs England comparison. Plan 4: higher threshold, 30-year write-off. Plan 5: lower threshold, 40-year write-off
- [Plan 2 vs Plan 4](https://studentfinancecalculator.co.uk/compare/plan-2-vs-plan-4): England/Wales vs Scotland. Different thresholds and write-off terms
- [Undergraduate vs Postgraduate Loans](https://studentfinancecalculator.co.uk/compare/undergraduate-vs-postgraduate): Comparison of repayment rates (9% vs 6%), thresholds, and combined loan scenarios

## Scenario Analyses

- [Student Loans on £25k Salary](https://studentfinancecalculator.co.uk/compare/student-loans-25k-salary): Ready-made scenario showing monthly repayments and balance projections for each plan at £25,000 income
- [Student Loans on £50k Salary](https://studentfinancecalculator.co.uk/compare/student-loans-50k-salary): High-earner scenario. Shows accelerated repayment and interest impact at £50,000 income
- [Career Progression Impact](https://studentfinancecalculator.co.uk/compare/career-progression-impact): How typical salary growth paths (gradual vs rapid) affect total repayment and loan duration

## Resources & Reference

- [Glossary](https://studentfinancecalculator.co.uk/resources/glossary): Complete glossary of student loan terminology (RPI, threshold, write-off, PAYE, SLC, etc.)
- [Plan Finder Tool](https://studentfinancecalculator.co.uk/resources/plan-finder): Interactive tool to determine which loan plan applies based on course start date and location
- [Threshold History](https://studentfinancecalculator.co.uk/resources/threshold-history): Historical repayment threshold data for all plans showing annual changes
- [Interest Rate History](https://studentfinancecalculator.co.uk/resources/interest-rate-history): Past and current interest rates for Plan 1, Plan 2, and Postgraduate loans

## Regional Information

- [England (SFE)](https://studentfinancecalculator.co.uk/resources/regions/england): Student Finance England information, contact details, and England-specific rules
- [Scotland (SAAS)](https://studentfinancecalculator.co.uk/resources/regions/scotland): Student Awards Agency Scotland information and Scottish loan plan details
- [Wales (SFW)](https://studentfinancecalculator.co.uk/resources/regions/wales): Student Finance Wales information and Welsh student loan rules
- [Northern Ireland (SFNI)](https://studentfinancecalculator.co.uk/resources/regions/northern-ireland): Student Finance Northern Ireland information

## International & Expat Resources

- [Moving Abroad Overview](https://studentfinancecalculator.co.uk/resources/international/moving-abroad): General guide for UK graduates relocating overseas. Notification requirements, overseas thresholds, payment methods
- [USA Expat Guide](https://studentfinancecalculator.co.uk/resources/international/usa): Specific guidance for UK graduates living in the United States. Repayment obligations, currency exchange, SLC contact
- [Australia Repayment](https://studentfinancecalculator.co.uk/resources/international/australia): Australian resident guide. Local threshold rules, payment processes, and enforcement
- [EU Country Guides](https://studentfinancecalculator.co.uk/resources/international/eu): European Union repayment information. Post-Brexit rules and EU-specific considerations

## Optional

- [About Page](https://studentfinancecalculator.co.uk/about): Mission, methodology, and team information
- [FAQ](https://studentfinancecalculator.co.uk/faq): Frequently asked questions about student loans and the calculator
- [Contact](https://studentfinancecalculator.co.uk/contact): Get in touch for questions, feedback, or partnership inquiries
- [Privacy Policy](https://studentfinancecalculator.co.uk/privacy): Data handling and privacy practices (no user data stored, analytics disclosure)
- [Terms of Service](https://studentfinancecalculator.co.uk/terms): Usage terms and legal disclaimers
- [Cookie Policy](https://studentfinancecalculator.co.uk/cookies): Cookie usage (analytics only, no advertising cookies)
- [Disclaimer](https://studentfinancecalculator.co.uk/disclaimer): Financial advice disclaimer and calculation accuracy notes