I'd be careful about how you word that. They are predicting the average return of US equities would be about 1% lower over the next 20 years. Compound interest

I'd be careful about how you word that. They are predicting the average return of US equities would be about 1% lower over the next 20 years. Compound interest over time is what means you have to save twice as much to end up with the same amount of savings.