I would not recommend at all that it gets to such a stage where your father has to "force" you to give him a percentage of your income. You should be honoured and more than obliged to give your father what you are able to.
In Islamic law, nafaqah on your father is wajib. Your parents who gave you life, nurtured you, accommodated for you and educated you, the least you can do is give back to them a portion of what you have.
Yes, you need to make your own financial plans, and plan for your future, as that is also important. You might be reluctant to give to your father if he has an addiction, like gambling or something else that is haram. In these kind of circumstances, you can financially contribute to his life, but not by giving cash.
But if this is not the case, then maybe your father is financially struggling, or saving money for you, or teaching you loyalty to parents by giving away what we love the most: "money".
Give to your parents, and you will immediately see the showing of blessings and fortunes onto you. This is what Islam guarantees.
With prayers for your success.