Lump Sum Decision Calculator

Student loan, mortgage deposit, or invest?

Got a lump sum — an inheritance, bonus, or trust payout? This is one of the most common questions on r/UKPersonalFinance. This tool models all three options with real UK figures so you can compare. Free, instant, no sign-up.

✓ Student Loan write-off modelling✓ LTV rate comparison✓ ISA + GIA tax modelling

⚠️ This tool is for educational purposes only — not financial advice. Consult a qualified, FCA-regulated adviser before making decisions.

Frequently Asked Questions

It depends on whether you'd actually repay the full balance. If your salary means you'll never clear the loan before it's written off, paying it off early means you're voluntarily repaying money you'd never have had to pay. Use this calculator to check. For most Plan 2 borrowers with balances above £40k, letting it run and being written off is financially better. See the UKPF Student Loans guide for a thorough breakdown.

Loan-to-Value (LTV) is how much you borrow as a percentage of the property price. Lower LTV = less risk for the lender = better rates. Key thresholds are 95%, 90%, 80%, 75%, and 60%. Crossing one of these thresholds with a bigger deposit can save you thousands in interest over the mortgage term. The UKPF Mortgage Overpayments vs Investments guide explains this in detail.

It depends on the interest rate of the debt vs your expected investment return. Student loans are unusual because they're written off after 25–40 years and repayments are income-contingent. Mortgage debt has a guaranteed interest cost. Investments have uncertain returns but historically outperform mortgage rates over long periods. This calculator helps you compare all three with your actual numbers. For more context, see UKPF: Mortgage Overpayments vs Investments.

Plan 1: 25 years after the April you were first due to repay. Plan 2: 30 years after the April following graduation. Plan 5: 40 years. Postgraduate Loan: 30 years. After the write-off date, any remaining balance is cancelled — you owe nothing more. Check the UKPF Student Loans guide for the full details on each plan.

Mortgage overpayments give you a guaranteed, tax-free return equal to your mortgage interest rate. Investing in equities has historically returned more (7% nominal) but is not guaranteed and gains outside an ISA are taxable. If your mortgage rate is above 5%, overpaying is very competitive. Below 4%, investing often wins over longer time horizons. Your risk tolerance and need for liquidity also matter. See the full analysis at UKPF: Mortgage Overpayments vs Investments.