What this DDM calculator is measuring
The Gordon growth dividend discount model estimates what one share may be worth today if the next-year dividend is known, dividends are expected to grow at a stable perpetual rate, and investors require a specific return to hold the stock. In that narrow setting, value is the present value of a growing perpetuity.
This is a deliberately narrow model. It is best suited to mature dividend-paying businesses with relatively stable payout policies. It is not designed for companies with no dividends, unstable dividends, multi-stage growth, or heavy dependence on buybacks rather than cash dividends.