The rules that matter
You get one free transfer per gameweek. If you don't use it, it rolls over, up to a maximum of five banked. Any transfer beyond your free ones costs 4 points. Your squad is always 15 players (2 goalkeepers, 5 defenders, 5 midfielders, 3 forwards) within £100.0m, with no more than 3 from one club.
When you sell, you keep half of any profit since you bought the player, rounded down to the nearest £0.1m; a loss is taken in full. That is why your selling price can be lower than the price on the transfer screen.
Plan gameweeks, not one week
A transfer is judged over every gameweek you keep the player, not just the next one. Bringing in a forward before a run of easy fixtures is worth more than his next match alone suggests. Look three to six gameweeks ahead: far enough to see fixture swings, close enough that injuries and form haven't changed the picture.
Gaffer Maths' transfer planner does this with integer programming: it searches every legal combination of moves across the horizon, including which weeks to roll a transfer, under all the squad rules. By default it values a banked transfer at about 1.5 points, because a spare transfer next week has real value.
When a −4 is worth it
A hit pays off when the incoming player outscores the outgoing one by more than 4 points over the gameweeks you'd keep him. Expected points give the average gain, but the average hides the spread: a +5 expected gain can still lose you points four times in ten.
The hit check simulates the gameweeks thousands of times and reports how often the move comes out ahead, not just the average. A useful rule: take a hit when the expected gain is well clear of 4 and the move pays off in most simulations; roll the transfer when it is marginal.
For the template team (the most-owned legal squad), the best single move right now is Cherki → Mbeumo: +3.2 expected points over 3 gameweeks, ahead in 62% of simulations (good use of a free transfer). Load your own team for your answer.
Rolling transfers
Rolling a transfer is often the best move when nothing is clearly worth doing: two free transfers next week let you fix two problems without a hit. Rolling stops paying once you have five banked, because the sixth is lost.
A pre-deadline routine
1. Check injuries and flags in your squad. 2. Check price changes if you plan to buy or sell soon. 3. Run the planner over the next few gameweeks. 4. If a hit is suggested, run it through the hit check. 5. Set captain and bench last. The GW checklist does all five for your team from its ID, with no password.