How to model buying X every Y years? e.g. new car every 5 years?

You can use the Recurrence feature to define patterns for how things should repeat over time.

For example, to model buying a new car every 5 years, you could add a new car to your plan starting at a specific year or milestone. You could set the sale date on that car to 5 years later, and then add a Recurrence to repeat this as a pattern with 0 years in between (so the old car is always sold in the same year the new one is bought).

Note that recurrence patterns can currently only be defined for “new” items added to your plans, rather than items already owned as part of the plan’s starting conditions. (This is because the simulation engine needs to know exactly how future instances should be financed).