GPT-5.3-Codex vs Grok 4.5for everyday maths

Because early overpayments cut the loan balance sooner, and interest is charged on whatever balance remains each month. So that £100 doesn’t just reduce debt once — it keeps reducing future interest year after year. In the final 5 years, there’s much less time left for that “interest on a smaller balance” effect to build. Same £100 paid late still helps, but it has far fewer months to create extra savings.

Overpaying early slashes the large starting balance sooner. Interest builds on whatever you still owe, so cutting the debt early prevents decades of interest from accumulating on those extra payments. Near the end the balance is already tiny and little time remains, so the same £100 saves almost nothing.

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