I'm using minoxidil twice and finasteride 1 pill daily. Can I reduce minoxidil usage after reaching my goal? Like once a day?

Thank you for your question. I suggest that you move forward and consult with a board certified facial plastic surgeon who has expertise in hair regrowth. You can develop a treatment plan, which may include NeoGraft Hair Restoration because it is the most effective natural regrowth method.
Best wishes,

If minoxidil is helping you and you have no side effects, the  cutting the dose in half will likely lead to hair loss. However, if the minoxidil is not helping you, then cutting it in half or even stopping it altogether will have no effect. See an expert for thorough review.

it is totally ok to use minoxidil 5% once a day only. I just recommend for you to keep using finasteride continuously.