The annual allowance is the maximum amount that can be paid into a pension each tax year, without paying tax. The cap since 2016 is £40,000. This includes all contributions made to your pension pot made by you, your employer, or any third party. Any contributions above this limit may be subject to a tax charge known as the annual allowance charge. You can contribute up to 100% of your UK earnings into a pension and receive tax relief, if you earn less than £40,000.
So, if your gross salary is £35,000, you can contribute up to a maximum of £28,000 into your pension (£35,000 minus basic rate tax).