Goals & planning
Prepayment cash-buffer comparison
Prepaying saves interest but spends liquidity. Three amounts side by side: how many months of living costs remain, and how much the payment drops.
Reading the table
monthly expense already contains the mortgage payment
Three columns compared
| No prepay | A：100,000 | B：200,000 | |
|---|---|---|---|
| Cash left | 300,000 | 200,000 | 100,000 |
| Months covered | 20.0 | 13.9 | 7.2 |
| Monthly payment | 4,680.89 | 4,095.78 | 3,510.67 |
| Payment change | 0.00 | -585.11 | -1,170.22 |
| Months left | 240 | 240 | 240 |
| Net interest saved | — | +40,426.75 | +80,853.50 |
| Penalty | 0 | 0 | 0 |
How 'months covered' is computed
Cash left ÷ monthly essentials = months covered. With 'expense includes payment' checked, post-prepay outflow is expense − current payment + new payment; unchecked, the payment is added on top. The two conventions never double-count the mortgage.
Interest saved is modelled on the lower-payment route — it is the one that directly improves cash flow. The shorter-term route keeps the payment unchanged and does nothing for the near-term buffer.
Why there is no 'should you' verdict
Whether to prepay depends on income stability, other debt rates, investment options and tax rules — none of which are inputs here. The tool lays out the liquidity consequence of each amount; the decision is yours.
Frequently asked
Should 'monthly essentials' include the mortgage?
Match the figure you enter. If it already contains the mortgage payment, check 'includes payment' and the tool swaps in the new payment; if it is living costs only, leave it unchecked and the payment is added on top.
Why model savings on the lower-payment route?
This tool is about how long your cash lasts. The shorter-term route keeps the payment unchanged and does nothing for cash flow; the lower-payment route cuts the monthly obligation directly. Compare both routes on the mortgage prepayment calculator.
What does a red months-covered figure mean?
That column's cash falls short of your buffer target under the new payment. It is a flag, not a veto.
What if an amount exceeds the balance?
It is treated as paying off the loan: payment drops to 0 and the saving is all remaining interest minus any penalty.
Months covered is a static estimate — income changes, rate resets and lender rules are outside the model. It compares numbers only and does not recommend whether to prepay.