Changing your return rate assumption in CostMe

When CostMe shows what a price could grow into, it has to assume a yearly return. The default leans on the long-run history of the US stock market. Roughly 10% a year before inflation. Here is what that means and when you might want to change it.

What the return rate is

The return rate is the growth CostMe applies each year to turn a price into a future number. A higher rate makes the projected value bigger; a lower rate makes it smaller. It is the engine behind the 30-year value you see.

Why the default is what it is

The broad US stock market has returned about 10% a year on average over the long run, before inflation. That is a historical average, not a promise. Some years are up, some down, and the future is never guaranteed. CostMe uses it because it is a familiar, defensible starting point, not a prediction.

When to change it

1. Want to be conservative? Lower the rate. A smaller number is still a strong nudge and harder to argue with.
2. Hold mostly bonds or cash? Set a rate that fits what you really earn, not a stock-market average.
3. Curious how sensitive the result is? Nudge it and watch the projection move. It teaches you how compounding works.

Keep it honest

A rate that is too rosy makes every skipped purchase look like a fortune, and your gut stops believing it. Pick a number you can defend so the savings story stays credible.

The takeaway

The return rate is the assumption under every projection. The default uses the market's long-run ~10% history; lower it if you want to stay cautious. Either way, the lesson. Small buys add up . Does not change.