To model a large, one-off partial repayment of a mortgage (not a debt payoff, which is even easier to do):
1. First add two events to the timeline. You can add an event either by going to the Time screen or, on any of the data entry screens, select the Time panel > Event tab and click the New Event button.
2. Drag and drop an event onto the timeline in the year the overpayment is to occur. Name it "Mortgage Paydown", for example.
3. Place a second event in the following year of the plan. Name it "Resume Regular Mortgage Payment", for example.
4. Go to the Debt screen.
5. Select the Mortgage item in the ledger.
6. Next, expand the Step Up / Step Down panel in the Advanced Settings.
7. Select the first of the two events to schedule the overpayment. Enter the stepped-up payment amount. Inflation rate can be left as is. Enter the full increased debt payment amount.
Another set of fields will display automatically on the Step Up / Step Down panel allowing you to enter an additional step.
8. Select the second of the two events and enter the regular mortgage payment amount, stepping it down to the usual amount in the year following the overpayment.
9. Click Update to save these changes.
Check the details of the Let's See chart to verify that this is being modelled as expected.
Other possible ways to use lump sum inflows proactively within a plan include:
Cash Flow Basics - An introduction to the basics of cash flow in Voyant