The Cardano staking calculator is only used as a guide of what you could potentially earn as a reward for being a delegator to a pool. The calculator here is by no means an exact and accurate indication of your return on ADA. Various factors such as a pool's luck factor and performance will affect the pools ability to produce rewards for your delegation. For example, a pool that isn't allocated many blocks will have fluctuating rewards and luck value purely determined by the network. A pool that misses blocks or is not performing as expected may mean you need to move pools.
If you enjoyed this calculator, please consider delegating to STICK Pool