Treatment of Personal Pension Contributions

Ref question 207- Dembe This is what the answer quotes: "Before making the personal pension contribution, Dembe's adjusted net income of £130,000 exceeds £125,140,so no personal allowance is available.The personal pension contribution will reduce Dembe's adjusted net income to less than £100,000 (130,000– 40,000 =90,000), so the personal allowance will be fully reinstated." I would like to know if it's a fixed thing for the personal pension contributions to be deducted from the income to get the chargeable income while also increasing the basic band threshold for 20%?