Britain's Queen Elizabeth views the interior of the refurbished East Wing of Somerset House at King's College in London February 29, 2012. Reuters Queen Elizabeth II will become the longest serving monarch in British history on September 9.

After taking the throne on February 6, 1952, she will beat Queen Victoria’s record of 23,226 days, 16 hours and 23 minutes.

It's received wisdom in the British media that the royals are somehow good for the economy.

And according to new data from specialist brand and business valuation agency Brand Finance, her reign has raked in a sizeable amount for the British economy — although the net contribution is a lot less than you think.

Brand Finance said that at the time of Queen Elizabeth’s Diamond Jubilee in 2012, the Monarchy’s value at that point to be in excess of £44 billion ($67 billion). Three years on, its value now rests around £57 billion ($87 billion).

However, Brand Finance estimated that the Royal Family's net contribution to the UK economy is around £1.155 billion ($1.8 billion) for this year.

Basically, a bulk of the upside the Royal Family provides in tourism and sales is cancelled out when you take into account how much it costs to look after them.

Costs such as the Sovereign Grant, security and maintenance of palaces, are netted off against sources of income including the uplift to the tourism, the price premium commanded by brands with Royal Warrants, and the surplus generated by the Crown Estate.

Here's Brand Finance's break down of the figures:

And here are the monarchy's asset holdings: