Do I need to register for VAT if I earn under the threshold?

If your VAT-taxable turnover stays below the registration threshold, currently £90,000, over any rolling 12-month period, you don't have to register, though you can choose to register voluntarily. You do need to keep tracking your turnover on a rolling basis (not just by tax year), because once you're forecast to go over the threshold in the next 30 days, or you've exceeded it in the past 12 months, registration becomes compulsory. It's worth reviewing your turnover monthly so you're not caught out and can register in good time.