A soldier earns experience during combat. After the mission, the soldier will then earn a random amount of stat increases based on what experience the soldier acquired during combat.
Experience, in X-COM, is the accumulation of combat experience by successfully performing actions. After combat, this experience is applied towards the improvement of stats.
This article discusses how experience is earned and how it affects a soldier's stats.
How Experience Points Are Applied
Soldier stats can be divided into two areas, primary and secondary stats.
- Primary Stats are stats that are directly influenced by the actions that they are associated with. Henceforth these actions will be known as Primary Actions. The following is a list of Primary Stats:
- Every time a Primary Action is taken, Primary Skill Points are earned. They count the number of successful primary actions taken. This is used to calculate how much experience is gained at the end of combat. Refer to the individual stat pages by clicking on the links above for the specifics on each stat.
- The number of primary skill points you earn at the end of a mission relies solely on the number of primary actions you perform during combat, and random chance. Your current skill level doesn't matter. It doesn't matter if you have the lowest recruit value, or you're one point below the cap.
- Points assigned have a stairstep function, corresponding to a range within which points are rolled. The range increases as more actions are performed:
| Ave. Inc. /|
|1 - 2||0 - 1||0.5||0.50|
|3 - 5||1 - 3||2.0||0.67|
|6 - 9||1 - 4||2.5||0.42|
|10+||2 - 6||4.0||0.4|
*Successful Psi actions count as 3 actions - see below *Bravery does not pay heed to this table at all - see below
- Performing more than 10 actions won't cause any more increase. Once you reach that figure you get a 2-6 roll and that's that.
- As you can see, there are distinct breakpoints at 3 actions and 10 actions, corresponding to an average increase of 2 and 4 skill points, respectively. Three actions are the best "bang for the buck", if you have a limited number to spread across your squad (a.k.a., a limited number of aliens to kill). It's not an issue with psi or throwing (which you can do all you want), but is for other primaries. Of course, when a unit is near its cap, you should always aim for the biggest boost for that final roll.
- Related to this, letting your soldiers throw 3 times just before ending a mission maximizes Throwing Accuracy growth vs. your personal time spent. (If you give a damn about Throwing!)
- In a sense, more than 3 actions wastes those actions, unless you can get to 10 actions. (Arguably, getting to 6 is an exception, especially if you find yourself at 5 actions after e.g. some reaction firing.) Unless you have plenty of targets (so that many soldiers can make it to 10 actions), try to stop at 3 actions. Either count bullets as a crude approximation, or use a utility that reads the UNITREF.DAT experience counters from a saved game for exact counts. The number of bullets you've shot will accurately reflect your Reaction counter (unless the person also did direct fire sans reacting), but knowing how many hits were landed for Firing Accuracy can be much more problematic. For a little more detail on efficiency versus experience, see this.
- Psi actions are a special case. Successful panic or mind control (MC) attempts cause the psi experience counter to go up by three actions. Thus, you only need to do 4 successful MCs or panics to get all the psi skill points you're going to (4x3=an experience count of 12). But unsuccessful attempts only cause the counter to go up by one. So you need 10 failed attempts to get to the 2-6 roll range, just like for all other primary stats.
- Throwing Accuracy is also an oddball. While it follows the rules for all primaries (except Bravery), it only increases your Throwing Accuracy. It does not trigger secondaries to increase. (It would've been too easy to increase stats, otherwise! Actually, Psi is just as easy to develop, but it takes time to research psi, and then it needs more combats to reach its cap.)
- Performing more than 255 actions of a given type will cause all experience to be lost. This is known to be true for Psi actions, and is undoubtedly true for other actions as well as they are stored in one byte fields. Psi is the only place it's realistically likely. More precisely, experience gets wrapped around, and starts counting again. If you are seriously testing stats, or are challenging yourself by allowing only one psi person, the distance from 255 to 265 (255-10) is only 4.3%, or 3 to 4 MCs on top of 85 successful Psis (28 turns' worth, if they've been successfully MCing since Turn 1). Thus, this may sound scary, but you have nothing to fear unless you've had someone successfully MCing 3 times every turn, for 30 turns - and even then, just let them MC a few more. What's 10 more compared to 255?
- When you think about it, Ye Olde Programmers Of Yore made a simple and robust system where all squaddies are expected to participate, and hopefully each of them get to make a few primary actions that increase their score some real amount each combat mission.
Bravery experience can also be gained on the battlefield, but by a very different means from all the other primary stats. The bravery stat itself is stored in increments of 10 (10 minimum, 100 maximum, with 110 possible for certain non-human units), and it can only increase by 10 points following each combat (it either gains 10, or nothing).
To gain bravery experience, a unit must have its Morale reduced below 50, where it stands a chance of panicking or going berserk. If the unit successfully resists panicking, it will gain a "bravery experience" point. Each bravery experience point gives the unit an additional ~9% chance (or an eleventh, to be precise) of gaining +10 Bravery at the end of the combat. At 11 or more bravery experience points, the +10 Bravery gain is guaranteed.
Like other primary stats, gaining one or more bravery experience points during a combat triggers secondary stat increases.
- Secondary stats increase when one or more primary actions are performed (except for throwing). Secondary stats are:
- Secondary skill points work quite differently from primary skills: It does not matter how many primary actions are taken; all that matters is that you did one primary action (land a non-IN attack on an enemy, react to something, not panic when Morale is below 50, or use a psi attack) -- your secondaries will increase all that they're gonna. It also doesn't matter if you did more than one kind of primary action.
- The maximum possible increase falls steadily as your secondary skills approach their caps, down to an average of 1 point (range 0-2) per combat for each stat. This is actually a simplification; for a graph of skill increases vs. current levels, see here. Thus, secondary stats which start very low should increase quickly, and will then increase less rapidly as they rise. Rookies with the lowest possible starting stats will have the following as their max possible roll:
- The minimum possible roll is always zero for secondaries. Across the four secondaries, soldiers will show wide variations of luck or lack of luck following each combat, just like flipping coins. Still, the odds are that someone low will rise fast. It's real hard to roll a lot of zeros in a row when the maximum is two or more (and it always is).
- If a primary skill is over its cap, it does still trigger (non-capped) secondaries to increase, by performing it.
- The formula can be summed up as being a boost of 0 to (a tenth of the distance from the cap rounded down + 2). For example, if a soldier has 67 TUs, they're thirteen away from the cap, so the maximum possible TU boost they can get is 3 points (13/10+2 = 1+2 = 3). 50 TUs would be 5, 79 TUs would be 2. If a roll happens puts a unit above its cap, then so be it.
Given the rules of how experience works, one can predict how long it will take soldiers to advance their attributes.
Primary skill advances can be based on hypothetical soldiers who always get:
- Low experience: 3 primary-skill experience points leading to a 1-3 roll and thus, always an average of 2 points per combat
- High experience: 10 primary-skill experience points leading to a 2-6 roll and thus, always an average of 4 points per combat
Secondary skills likewise use an average roll for advancing, according to the decreasing-slope function described above.
Because you can select or reject soldiers based on their starting stats, the more important question becomes, "which stats take the longest to advance from recruit maximum to its cap?" In other words, values above recruit max can't be "bought"... so which have the farthest to develop and should be focused on, if you want to maximize your stats?
You can use this as a basis for keeping or rejecting new recruits, or otherwise choosing which skills to develop.
The table below shows the number of combats needed for a soldier to advance from recruit maximum to attribute cap, on average. A more detailed look, including starting from recruit minimum, theoretical min and max advancement times, etc., can be found here and a PDF of the same is here.
Putting It All Together
- While you might focus on the averages stated above, the actual points assigned are entirely random. The range is what you should expect for any one soldier on any one combat mission. This follows the usual X-COM behavior of defining a range and rolling randomly within it.
- Do your best to get every soldier you are interested in developing, to get at least one primary action (not including throwing). This will trigger secondary stat increases. Then try to shoot for the big breakpoints of 3 or 10 primary actions. Doing more than 10 actions does not increase a particular primary stat any more, so give other soldiers the chance to perform actions once your favorite soldiers have maxed out on theirs.
- Any soldier can (and will!) ultimately become a maxed-out superman. (EXCEPT for Psi-wimps, who will never improve at all) The worse a secondary stat is, the quicker it will rise. And you can try to target who performs which primary actions. Taking advantage of the breakpoints of 3 and 10 can also help you manage potential skill increases (a.k.a. targets) as effectively as possible. That said,
- Early in the game, don't spend much time or money fretting over stats. Any soldier is liable to come up snakes with their Psi strength. And every soldier can otherwise eventually become a superman.
- Once you have Psi on board, you can use Experience Training to optimize advancement.
- In the endgame (when you have tons of cash), if you're a micromanager role-playing to make soldiers who are maxed across the board, it's arguably more important to pick recruits who are not anomalously low in any one stat, rather than ones who are high in a few things. In other words, if your goal is 100% stats, one really bad stat may slow you down more than e.g. being a particularly good newbie shooter. Firing accuracy, reactions, and stamina have the biggest span between recruit values and work needed to max them out.
Every soldier statistic has a maximum allowed value, as shown in the table below. Your soldier will eventually have a value equal to or slightly greater than the cap. It is allowed to go over the cap, the very last time you have a combat while it is still under the cap. For example, the maximum Firing Accuracy is 120. If you go into a combat at 119, do lots of shooting, and get a +5 roll, you will walk away with 124 Firing Accuracy - but it will never increase again.
Primary skills can overflow their cap by 5, and secondary skills can overflow their cap by 1, as shown here:
|Primary Stat||Min Cap||Max Cap|
|Psi Skill||100||105+ *|
|Secondary Stat||Min Cap||Max Cap|
* Psi Skill is an exception. Psi Lab training can continue to add 1-3 points each month after reaching the cap, and will loop the value back down to 0 if it passes 255.
You have a 33% chance of getting capped at Cap+1 for secondary skills, and you have no control over what happens (barring reloading your game and ending combat again). The chance is 33% and not 50% because there are two ways to reach Cap (being at Cap-2 and rolling 2 or being at Cap-1 and rolling 1), but only one way to reach Cap+1 (being at Cap-1 and rolling 2).
For primaries, a soldier that does 10+ actions (for a 2-6 roll) every single combat mission will get Cap+5 in that primary skill 5% of the time, on average. "Every single mission" means, without regard for the fact you're nearing the cap (and playing with the possible roll results). You can increase the odds to as high as 20%, if you use the primary increase roll ranges to inch your way up to Cap-1, then do 10+ actions on your final combat. Or you can have a 0% chance of Cap+5 if you don't pay attention and don't do 10+ actions near the cap!
Experience training outside combat
- With the exception of Psionic Skill training in the Psi Lab, all stats can only be trained through combat experience.
- A Rookie that has gained any experience except throwing, is promoted to Squaddie (also see promotions).