を前提(ぜんてい)にOn the premise of

Both refer to using information as a basis, but the stance is different. を前提に means ‘on the assumption that’ and treats something as a condition that must be accepted before proceeding, often hypothetical or conditional, as in 雨が降ることを前提に計画を立てる ('We make the plan assuming it will rain.'). を踏まえて means ‘taking into account’ and is used after facts or results that are already known, emphasizing reflection or consideration rather than assumption, as in 調査結果を踏まえて方針を決めた ('We decided the policy taking the survey results into account.').

Both indicate a basis, but the type of basis differs. を前提に sets a condition or assumption that must hold true, often before action is taken, as in 合意があることを前提に話を進める ('We proceed with the discussion on the assumption that there is agreement.'). をもとに means ‘based on’ and refers to concrete materials, data, or sources actually used to create or decide something, as in 実話をもとに映画が作られた ('The movie was made based on a true story.').