GPT-5.6 Sol vs Grok 4.5for everyday maths

Mortgage interest is charged on the amount you still owe. Overpaying early reduces that balance for many years, so you avoid interest on the overpaid amount throughout most of the mortgage. It also means more of each later payment goes toward clearing the remaining debt rather than interest. In the final five years, the balance is already much lower and there is little time left for interest to build up, so identical overpayments save far less.

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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