What the discount rate is doing
Discounting converts money expected in the future into today's dollars. The higher the discount rate, the lower the present value of those future cash flows. The lower the rate, the more heavily the future amounts count in today's valuation.
This calculator turns that idea around. Instead of choosing the rate first, it solves for the discount rate that would make the future cash flow or evenly spaced cash-flow series match the present value you enter. That makes it closer to an implied return or internal-consistency check than a basic present value calculator.
The solved rate can be compared with a benchmark or hurdle rate. If the implied annual discount rate is well above your benchmark, the present value is conservative relative to that hurdle. If it is below the benchmark, the valuation may rely on accepting a lower return than your usual opportunity cost.