Tax relief on one off pension contributions - net or gross

I am looking to keep my taxable pay to under £100k, as I have two children in nursery and benefit from funded hours. My annual salary is £106k, which I offset by paying into my pension via salary sacrifice. However, I received an additional bonus earlier this year of roughly £29k, which was processed via payroll. I am looking to help keep under the £100k threshold for this tax year by making a one-off pension contribution. My main question is whether the figure I should be using in my calculations is the net figure I pay into my pension or the gross figure, which is the net figure plus the 20% tax relief instantly applied? I want to make sure that I get this right, so as not to lose funded hours benefits going into next year.

Hi,
Please follow the guidance at
Personal Allowances: adjusted net income
Thank you