Start with the 50/30/20 rule
If you don't know where to begin, split your take-home pay three ways:
- 50% needs — rent/mortgage, bills, food, transport, minimum debt payments
- 30% wants — eating out, subscriptions, hobbies, treats
- 20% savings & debt — emergency fund, overpaying debt, pensions, investing
It's a starting point, not a straitjacket. If your rent is high, your "needs" slice will be bigger — the point is to give every pound a job.