If your business makes Vatable and exempt sales, you will already be subject to partial exemption and should be preparing calculations for partial exemption for every VAT return.
Under MTD you continue to prepare the same calculations.
However, under MTD you will need to make these adjustments in your software so that you can file your return directly to HM Revenue & Customs from your software.
If you use accounting software and you currently make manual adjustments on a printed copy of a return or work out your final figures in Excel before filing them on the HM Revenue & Customs website, you will need to enter these adjustments into your software directly before filing your return.