The UK's First Past The Post electoral system means that a huge number of people live in constituencies in which the party they like best has very little chance of actually winning.
Tactical voting, put simply, means that individuals cast their vote for a candidate they wouldn't normally support to stop an undesired candidate from winning.
These sites, however, often disagree with each other, can be fairly opaque in how they make their recommendations and seem to neglect the idea that the other side might be voting tactically too.
This can often lead to a certain amount of confusion and romanticism when interpreting the extent to which tactical voting will make a difference.
With the candidate lists confirmed for the 2019 general election, we've put together our own - realistic - tactical voting interactive to give you a clearer picture of whether it could affect your seat. Subscribe below to get your personal recommendation.
How we came up with our tactical voting recommendations
In order to come up with recommendations for how to vote in the upcoming election, we analysed historic voting records for previous general elections.
By looking at the last two general elections in particular, we are able to assess each parties’ chances of actually winning a particular seat.
After classifying each party on Leave or Remain grounds, we then present you with the party which suits your own preference on the Brexit debate and has the best chance of claiming that particular seat.
In 542 seats, we don't believe this tactical voting will make a difference, due to the whopping majorities that the Labour and Conservative parties have. However, in other more marginal seats, a swing of just a few percentage points can make all the difference between winning and losing.
Below, we outline the criteria for how we decide if a party is a realistic choice for you.
If you're a Brexiteer
There are four parties across Britain and Northern Ireland which back Brexit in some form and have a realistic chance of winning at least one constituency.
There are the criteria which decide whether we advise you to vote for each individual Brexit-backing party.
If the Conservatives haven’t won the seat since at least 1992 (or since constituency creation);
If Ukip beat the Conservatives, and gained a vote share of over 20 per cent, in 2015;
And if the Conservatives got less than 30 per cent of the 2017 vote.
Any other seat in England, Wales or Scotland, where the Brexit Party do not have a realistic chance (as per the three criteria above).
If in Northern Ireland and the DUP are standing in that constituency.
The DUP have stood down in a select few seats for the UUP. In these seats, Brexiteers' best choice is the vote for the compromise-Brexit UUP.
If you're a Remainer:
There are seven parties across Britain and Northern Ireland which have some form of Remain-leaning policy and have a realistic chance of winning at least one constituency.
There are the criteria which decide whether we advise you to vote for each individual Remain-backing party.
If in Scotland and SNP currently hold the seat;
If in Scotland, Conservatives hold the seat and no other party is in sight.
If in Wales and Plaid Cymru already hold the seat.
If the seat is already Lib Dem-held, and the Tories are in second place;
If the seat is already Lib Dem-held, and the SNP are in second place - this depends on your stance on Scottish independence;
If the Conservatives hold the seat but the Lib Dems are in second place;
If the Lib Dems are the party that the Remain Alliance have put forward, and the combined vote share for the parties in the pact are ahead of Labour.
If the seat is already Green-held.
If Labour holds the seat with a majority of over 10 per cent;
If in Scotland, Labour holds the seat, the SNP are in second place but the Conservatives are within 10 points of the winner;
If no other explicitly Remain party has a realistic chance of winning the seat (based on the criteria above);
If the Lib Dems are within five points, then recommend both Labour and Lib Dem. If there’s a pact , then look at the combined vote share of the participating parties and if it’s ahead of Labour, recommend them.
If in Northern Ireland and SDLP is in second place;
If SDLP has the largest vote share out of SDLP and Alliance, and there is a realistic chance of them taking the seat (instead of DUP or Sinn Fein).
If in Northern Ireland and Alliance is in second place;
If Alliance has the largest vote share out of SDLP and Alliance, and there is a realistic chance of them taking the seat (instead of DUP or Sinn Fein).
We have accounted for the fact that not all parties are standing in every area, and only present realistic options.
Tactical voters are likely to cancel each other out
As many as 24 per cent of voters are intending to vote tactically at the forthcoming general election, according to a recent poll by BMG.
This is an increase on the 20 per cent who said the same thing when polled by the same company in the build-up to the 2017 general election, indicating that it could be a slightly bigger deal this time around.
However, when examining the breakdowns in these tables it appears likely that any voters voting tactically along a Leave/Remain axis will broadly cancel each other out.
Remainers - at 28 per cent - were slightly more likely to say they intended to vote tactically than Leavers - 22 per cent - and, although this will have varying impacts across different constituencies, the gap between the two is in most cases going to be too small to swing the result of a constituency.
It's far more likely that electoral pacts will have an impact.
The Liberal Democrats, Greens and Plaid Cymru have agreed not to field contesting candidates in 60 seats, while the Brexit Party are not competing in any of the 317 seats the Conservatives won in 2017.
By not standing candidates in certain seats, parties are effectively forcing voters to vote tactically although the extent to which this can be considered tactical voting is questionable.
Our analysis shows that around 53 Leave seats and 55 Remain seats could switch if people vote tactically.
If this plays out how we think, in all likelihood such Brexit-based tactical voting will just cancel each other out.