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Do you have a handy chart that shows all the calculations based on "accepted" numbers for ROI, SD, etc?
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There are a few worked examples in
this post. However, you should not assume that those are your win rates. It's ok (but not ideal) to assume that those are your standard deviations.
A lot of threads in the BBV forum are about some huge breakeven or losing stretch someone had that should be quite rare if the player is a solid winner. Much of the time, the person has not first established that he is a solid winning player at that level, and he may not be beating that level at all. (E.g., the player says he was beating NL $25 on Party, then moved to NL $50, on PokerStars, then dropped down to NL $25, still on PokerStars.) It would be extremely unlucky for an expert like Jennifer Harman to have a losing year in LHE. It's not a surprise if a random player does.
Sadly, many people have been fooled by an upswing into thinking that they could turn pro, and played in games they couldn't beat, much less beat for enough to make a decent living. That doesn't end well.
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I am guessing that if SnG's offer a typical ROI and SD we should see a typical BR requirment. Or is that where the 100 buy-ins come from?
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I'm afraid that gives a bit too much credit to the group. The SD for 9 or 10 player SNGs is about 1.7 buy-ins, but the ROIs vary widely. As with many other groups, the bankroll requirements recommended by SNG players do not depend on the win rates, but they should. If your ROI is 30%, you only need 1/6 of the number of buy-ins as someone with a ROI of 5%. 30% is greater that the STT FAQ says is achievable in $6 turbos, but it is achievable when playing a few low stakes non-turbos at a time.
When an expert who has a 5% ROI while playing 16 high stakes SNGs at a time tells you his downswings, it doesn't mean you will see anything similar if you have a 20% ROI playing low stakes SNGs. He may play better and he may be making more money per hour on average, but you will tend to have smaller downswings (in buy-ins) than the expert by a factor of 4.
So, if the consensus is 100 buy-ins, that will be overly conservative for some people, and overly aggressive for others. Even for the same person, it is likely that it will be overly conservative in low stakes games, and overly aggressive in high stakes games.
Another source of bad bankroll advice is Chris Ferguson. He might be a great player, but he should have known better than to say you can play with 20 SNG buy-ins or 20 NL cash game buy-ins. The latter is much more conservative than the former, unless your SNG win rates are ridiculously high, or cash game win rates are quite low. A lot of low stakes players will want to have something like 15 buy-ins for NL and 50 for SNGs. However, because he is a poker celebrity, people will repeat his advice for years and cite his 1.5 year journey from $0 to $10k, while others have quietly gone from $50 to $10k in a few months while using better bankroll management.
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If I am a beginner or someone who has been playing for a few years without tracking my results I won't know my ROI or SD, correct? I would need hundreds of thousands of hands logged in PT to know for sure.
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If you are a beginner, you shouldn't assume you are a winner. It's better to assume that you are a losing player, and set a budget until you have some experience.
You never know your exact stats. You always have to make some estimates, and you should update your estimates periodically. Over time, your estimates will gradually get more accurate, but game conditions can deteriorate, or you can learn to play better.
Your standard deviation is less sensitive to your playing style than your win rate is, and you can get accurate estimates much more rapidly, after only a few thousand representative hands (say with representative stack sizes and table conditions).
Formulas like bankroll = comfort * (standard deviation^2)/ (win rate) are still useful in several ways, even without perfectly accurate estimates. For example, you might determine that you would need an extremely high win rate to be comfortable playing game X on your current bankroll, and if the required win rate is higher than what the experts say is achievable, you probably do not want to take a shot at that game.
It's natural to assume that your win rate will decrease as you move up to tougher games. Even if you don't know your win rate in the higher stakes game, you might be able to say that it's not right to move up even if your win rate does not drop. This actually happens often when marginal winners take a long time to accumulate 20 buy-ins for the next level or whatever they have heard is appropriate. Because their win rate is low, they need more buy-ins to move up even if their win rate does not drop.
You can use the risk of ruin formula ROR ~ e^(-2*comfort) ~ 1/7^comfort on
pieces of your bankroll to measure the improbability of downswings based on assumptions of various win rates. Maybe you are so conservative that you want 25 buy-ins even in a soft game you think you can beat for a good rate. However, that doesn't mean you can safely ignore a 5 buy-in downswing, if that downswing will only happen 1/10 of the time if you are winning at the rate you hope, but will almost always happen if you are a losing player. Such a downswing is evidence that you have some leaks in your game.
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However, how do I handle wanting to take the occasional shot at a bigger game? Say the wife and kids are away for a weekend and I want stay up all night and play in a 2000 player, $10 MTT just for fun and maybe if I run well, a nice cash.
Do I need to replace/deposit that $10 directly and leave my roll alone? Guess I am asking, is it OK to "gamble" with some of my roll on the very rare occasion? And if so, how often and how much?
Hate to think that my roll is only for one type of game at one type of limit.
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You can use the same bankroll for all games where you have an advantage, and on all sites. You do not need to have a separate bankroll for each game, and you do not need to worry nearly as much about losing $50 on one site if you have $500 elsewhere. Bankroll management is based on the assumption that losing everything is a disaster, not an inconvenience. Shifting money between sites is only an inconvenience, and between games it's not even inconvenient.
When you take a shot at a game you are not sure you can beat, or for which you are not safely bankrolled, you should view this as a withdrawal from your bankroll. If you are slightly underbankrolled, it is only a partial withdrawal, but it takes some work to determine the equivalent withdrawal. It's safe to view it as an expense.
If you make regular withdrawals from your bankroll, you should view this as decreasing your win rate. If you withdraw all winnings (not recommended), you should require a much higher comfort level than if you leave most of your winnings in your bankroll. A solid NL $100 player might be quite safe starting with $1500, but not if he withdraws all winnings. A schedule such as withdrawing half of all winnings over $2000 will mean that the player will not be wiped out by the first 15 buy-in downswing, and will probably have hundreds of buy-ins by the time the first 20 or 25 buy-in downswing occurs.