In Spanish, you say ‘Te lo haré saber’ to express ‘I will let you know.’
This phrase is straightforward and conveys your intention to inform someone in the future. The verb ‘haré’ comes from ‘hacer,’ which means ‘to do’ or ‘to make,’ and ‘te’ means ‘to you,’ implying that you will be the one delivering this information. It’s a polite way to assure someone that you will follow up with them later.