Will Hay

I've massively increased my salary sacrifice pension contributions for the final three months of the tax year. This will mean my taxable earnings will fall under the 40% threshold. As I'm sure I've paid too much tax, do I simply use the nett/gross method [gross sum dividend by 80 x 100] on tge oension section of a self-assessment return to make a claim for the tax overpayment? Thank you.