Big reward = more stars. Aim for 3–4 weeks of consistent daily tasks.
A bike is a big ask, and "maybe for your birthday" turns into weeks of pestering. A star goal turns that one big yes-or-no into daily progress your child can watch fill up.
How long should a bike take?At 4–6 stars a day, 100 stars is about 3–4 weeks. Keeping it in that range makes the reward feel earned but not impossibly far away.
What if they lose interest halfway?Show the star count filling up, and if needed add one easy daily action so good days feel good. Never reset the stars already earned.