ER Interest Savings Calculator

Compares a lifetime mortgage left to roll up in full against the same loan with a client making regular voluntary payments. Shows the real cumulative contribution and how much of the balance reduction is genuine interest saved, not just the payments themselves — the figure AdviseWise's cost-of-borrowing graph doesn't surface directly.

Case inputs

If you have the MER (Monthly Equivalent Rate) from the illustration, use that — it's the figure the lender actually compounds with each month (rate ÷ 12), so there's no rounding drift. AER is usually shown rounded to 2 decimal places, and converting back from that rounded figure can drift by a few pounds over longer terms. Use AER only when MER isn't available.
Only enter this if you know the specific lender's rule for this plan — allowances commonly run 10–12% a year, most are non-cumulative (unused allowance is lost, not carried forward), and the basis varies by lender. This check assumes non-cumulative, reset each plan year. Treat any flag as a prompt to verify against the plan's KFI/illustration, not a substitute for it.

This models voluntary partial repayments reducing the balance directly. Without the ERC-free check enabled, it does not consider lender allowances at all — the payoff point below is a maths result, not a guarantee it's penalty-free on any given plan.

Balance over time

Year-by-year breakdown

Year Roll-up balance Balance with payments Total contributed Balance saved Net interest saved This year's contribution ERC-free allowance Status