A small regular contribution can be easier to plan around than an occasional grand promise.

Reliability is worth more to whoever depends on you than size is. Something modest that arrives every month can be built into a plan, while a large promise that may or may not appear has to be treated as weather. People rarely say this out loud, because the grand offer is generous and it feels ungrateful to want less of it more often.

Set your giving, of money or time, at the level you could still manage in a bad month. Say what that level is so nobody has to guess. If you want to add more later, add it as a surprise rather than as a new expectation.