Being confident of this, that he who began a good work in you will carry it on to completion until the day of Christ Jesus. (NIV)

And I am convinced and sure of this very thing, that He Who began a good work in you will continue until the day of Jesus Christ [right up to the time of His return], developing [that good work] and perfecting and bringing it to full completion in you. (AMP)

Being confident of this very thing, that he which hath begun a good work in you will perform it until the day of Jesus Christ: (KJV)