Most brokerage sites these days provide some kind of expiration graph of their positions. That graph may be rudimentary or much more flexible and helpful.
Helpful, yes, if you intend to stay in a trade until expiration. Do you really want to do that? Some of us don't. I can remember ending on expiration Thursday with the SPX about twenty points away from the sold strike in a call credit spread. The next morning, the SPX jumped, but it got nowhere near my sold strike. I and a whole bunch of other people, however, were surprised to find out later that day, when the settlement value came out, that the SPX had settled about 25 points higher than its close the previous day and well above its open that day. My call credit spreads were five dollar in the money. Yikes. That was the last time I carried iron condors or credit spreads into expiration.
As weekly options traders can tell you, trades are harder to manage expiration week. As I've admitted previously, I prefer the paint-drying style of a monthly income trade while others can easily handle the adrenaline rush of a weekly trade.
If it's my intention or yours not to carry a trade into options expiration week, perhaps we shouldn't be focusing so strongly on the expiration chart. For example, let's imagine that on June 26, 2013, a trader wanted to enter a JUL13 (not a weekly) SPX butterfly, but was agonizing over whether to put the wings 50 or 70 points away from the central strikes. The 70-wide wings had wider expiration breakevens but that version of the butterfly had a mid-price of 29.30 while the 50-wides were priced a much cheaper 15.25. If that trader intended to exit the trade by the Friday before expiration, that trader had only 16 days left in the trade. How much difference would be found in the breakevens 16 days away? Let's ignore the tent-shaped expiration breakevens and reset the "today" line for 16 days in the future. The vertical lines mark the then-current price when this chart was snapped and the breakevens for 16 days into the future.
SPX 50-Point Wide Butterfly 7 DTE:
Breakevens seven days to expiration, when this trader plans to exit, are approximately 1557.30 and 1635.68.
SPX 70-Point Wide Butterfly 7 DTE:
Breakevens seven days to expiration, when this trader plans to exit, are approximately 1558.12 and 1639.00. They're not that much different than the breakevens for the fifty-wide butterflies, are they?
Obviously, in this case, the wing width made little difference in breakevens by seven days to expiration. Some butterfly traders tend to adjust either when the expiration breakeven is hit or perhaps halfway or two-thirds of the way between the peak and the expiration breakeven on that side. If the trader has no intention of holding the trade into expiration, it could be argued that the adjustment might be made in accordance with these new breakevens, not with the expiration breakevens. You can see from the comparison of those breakevens that there wouldn't be much difference in the adjustment points for the 50- and 70-point wide butterflies.
You weekly traders could argue something else. You could argue that I could have just used one of the weekly cycles. That's true, but my butterflies are generally started further away from expiration than in this example. I just wanted to use then-current prices for the nearest expiration in this monthly cycle rather than going through back testing.
Of course there are other considerations to help the trader make up her mind whether to buy 50-wide or 70-wide wings. There's the overall cost of the butterflies, the risk in the trade. She would be committing more money to the 70-point-wide butterfly trade. If price were to sit still all those next 16 days with implied volatilities also not changing, she would be paid more handsomely for her efforts by the 70-wide butterfly, but she would reap a bigger percentage gain on her expenditure with the 50-wide butterfly.
Neither of these butterflies seems inherently better than the other. As with all choices with strategies, there are tradeoffs to each. It may be, too, that looking beyond the default expiration break evens and thinking about how the trade will perform at the point you plan to exit may help you decide which choice is best or, as in this case, decide that there is no standout best choice.