How do I reclaim CIS deductions that have been taken from my pay?

If you're a sole trader, CIS deductions taken from you are set against your Income Tax and Class 4 National Insurance bill through your Self Assessment tax return, and any excess is refunded once HMRC processes the return. If you operate through a limited company, CIS deductions suffered are instead offset against your company's PAYE/NI liabilities during the year, and any balance can be reclaimed from HMRC after the tax year ends. Keeping accurate records of every CIS deduction (from payslips or statements your contractors should provide) makes this reconciliation much easier, so it's worth a bookkeeper tracking this monthly rather than at year end.