It has been accepted without question that the NHS faces a funding gap of £30 billion by 2021-21. This was the figure quoted in NHS England’s Five Year Forward View. The report’s authors claim that the figure was calculated separately by Monitor, NHS England and independent analysts. It has been widely quoted, almost as fact, ever since. But we should question this figure. Where did it come from? How has it been acted upon? What are the consequences of it being wrong?