A conversion chart, supposedly showing the modern-day worth of Jane Austen characters' fortunes, has surfaced on Twitter. At first glance, it seems to show that Mr Darcy's supposedly vast 1803 fortune in Austen's novel Pride and Prejudice, worth $331,000 per year in modern US dollars, might not in fact stretch to quite the luxury of his 19th-century lifestyle if Darcy was alive today.

But the figures are out-of-date: they actually come from an American academic paper published in 1989, and the value of the pound has changed dramatically since then. It turns out that, Mr Darcy's annual income of £10,000 in around 1803 would be worth £796,000 per year today.

That still probably wouldn't be enough to run a modern incarnation of Pemberley, his beautiful fictional stately home in Derbyshire, if its costs were anything like the costs of running real-life Derbyshire stately home Chatsworth House today (£4m per year).

In terms of spending power, Darcy would have been able to buy more with what he had. So his income, and in particular his financial power and influence, might be more faithfully translated using a measure that takes into account changes in GDP per capita, as well as the far greater gap between rich and poor that existed in the early 19th century. That figure works out at around £12m per year - enough to run three whole Chatsworths.

It's hard to say exactly how much Mr Darcy would have been worth in total, but the Duke of Devonshire, who currently lives in Chatsworth House, is estimated to be worth around £500m.

With so many different factors affecting value comparisons across the centuries, it's difficult to arrive at a reliable modern equivalent for Mr Darcy's fortune. But Mrs Bennett's enthusiasm on learning that Darcy is to be married to her daughter, Elizabeth, probably wouldn't be much changed if she found out her daughter was to share in a £12m per year 21st-century income.