GPT-5.6 Luna vs Grok 4.5for everyday maths

Mortgage interest is charged on the amount you still owe. An extra £100 paid early reduces your balance sooner, so you avoid interest on that £100 for many more years. Those savings can also reduce future interest, because each later interest charge is based on a slightly smaller balance. In the final five years, the balance is already much lower and there is less time left for the overpayment to prevent interest, so the same £100 saves far less overall.

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.

(58 words)