Lucky 7 is the pattern that draws a seven on the card: the whole top row, then a diagonal running from the top right corner back down to the bottom left. It is the best known of the shape patterns, mostly because everybody can already picture a 7 and no explanation is needed twice.
Which squares, exactly
Five across the top, then four more coming down the diagonal. The top right corner belongs to both, so it is counted once: nine cells in all.
Of those nine, one is the free space. The diagonal passes straight through the middle of the card, which is already marked before a number is called, so a player has eight squares to actually mark. This trips up hosts who count the drawing rather than the squares, and it is the difference between a round that ends when you expect and one that ends a call early.
How long it runs
Eight to fifteen minutes on a 5x5 card. That puts lucky 7 well above four corners and any line, and well below a blackout. It works best as a second or third round, once the room has the rhythm but before attention starts to go.
If you want it shorter, play it on a 4x4 card, where the shape is smaller and there is no free space to help. If you want it longer, follow it with the outside edge or a blackout.
Which way round
The standard shape runs the diagonal down to the bottom left, the way a written 7 goes. Some hosts allow the mirror image, so the diagonal runs down to the bottom right instead, and some allow either. None of these is wrong. What matters is saying which one you are playing before the round starts, because a player who has quietly been marking the other diagonal will not accept the answer afterwards.
Running it well
Show the shape rather than describing it. A printable pattern chart on the table settles the question of what the pattern looks like, which way it runs, and whether the free space counts, without you having to answer it four times.
Keep the call sheet, as with any pattern, so a shout can be checked in seconds.
How it compares to the other shape patterns
Lucky 7 sits in the same family as the letter X, the plus sign, the letter T and the letter L: patterns that draw something recognizable rather than following the traditional line. They all take longer than a line, and they are all easier to explain than they look, because a shape everybody can already picture needs no diagram.
Against the letter X, lucky 7 is about the same length, nine cells against nine, and both cross the center. The X feels harder because it needs both diagonals and a player watching one of them will lose track of the other. The 7 keeps most of its squares in a single row, which is easier to hold in your head.
Against the letter T, which is the top row plus the middle column, lucky 7 is the more interesting of the two to play. Both start with the full top row. The T then runs straight down the middle, which is easy to watch, while the 7 runs on a diagonal, and diagonals are the thing players consistently miss on their own cards.
Against the outside edge or a blackout, lucky 7 is short. If your evening needs a long finale, those are the patterns for it, and the 7 works well as the round immediately before.
A note on smaller cards
On a 4x4 card the shape still works: four across the top and three coming down, seven cells, with no free space to help. That makes it noticeably quicker and it is a reasonable choice for children, who tend to lose the thread of a fifteen minute round.
On a 3x3 card the shape stops reading as a seven, because a two square diagonal does not look like anything. Below 4x4, use four corners instead.
Cards to play it with
The bingo card generator prints unlimited unique cards free, with words or numbers. The full pattern chart shows lucky 7 next to every other common pattern, and bingo rules and winning patterns covers scoring, round length and the house rules worth agreeing first.