Understanding when to use formal and informal English is an essential skill for clear, confident communication. We adapt our language every day depending on the person, the situation, and the purpose. Whether you’re writing an email, messaging friends, preparing for IELTS, or speaking in professional settings, knowing the differences between formal and informal language will help you express yourself naturally and appropriately. This guide will walk you through key features of each style, examples used in British English, and practical tips to help you switch confidently between the two.