The guideline
Some investors use 1% of investable net worth as a maximum initial cheque for a single early-stage company. It is a risk-control idea, not a universal rule or a claim that the investment is suitable.
Look at the whole portfolio
One small cheque can still be too much when combined with other private companies, employer stock, or concentrated holdings. Decide first how much of the overall portfolio could be lost without affecting essential goals.
Allow for follow-on funding
A company may ask for more capital later. Reserving an amount equal to the first cheque would make the potential commitment twice the initial amount. Dilution, fees, taxes, and the inability to sell also matter.
Try a scenario
The Angel Cheque calculator compares the amount entered with net worth and existing exposure. A qualified adviser can assess suitability for your circumstances.