1. 4 Years - If you are in the first 4 years of your business and make a loss, you can use this loss to reduce your tax bill in the previous 3 years, such as from the job you had before you set up your business. You will receive a tax refund.
2. £5,725 - If your profits are lower than £5,725, you don't have to pay the annual £140 Class 2 NI, unless you need a credit towards your state pension. Ask for a repayment for earlier years.
3. £7,755 - If your profits are higher than £7,755, you will pay 9% Class 4 NI. This gets you no state benefits and effectively increases your tax rate from the 20% income tax rate to a total 29% tax rate.