Kelly only works if you update your bankroll constantly. Your bet size is a percentage of your current bankroll, not your starting bankroll. If you're up 30% on the season, your bets should be 30% bigger. If you're down 20%, your bets must shrink by 20%.
That sounds simple enough, but most bettors get this wrong. They calculate their Kelly percentage once, slap a flat dollar amount on every bet, and never look back. That's not Kelly. That's just flat betting with extra math. The entire point of the Kelly Criterion is that your wager size moves with your bankroll in real time, protecting you during losing streaks and accelerating your growth during winning runs.
Tracking your bankroll properly is the difference between a system that compounds your edge over months and one that blows up after a bad week. This page walks you through exactly how to do it, from building a simple tracking spreadsheet to knowing which metrics actually matter and when the numbers are telling you to change course.
Here's the thing most people miss about Kelly: it's a dynamic system. The formula assumes you're always betting a percentage of your current capital, which means every win and every loss changes your next bet size. If you're not tracking your bankroll after every session, you're flying blind. You might be betting 5% of last month's number when your actual bankroll has dropped 25% since then. That's a recipe for ruin.
Consistent tracking also forces you to be honest with yourself. When you see the numbers on a spreadsheet, there's no room for selective memory. You can't convince yourself that you're "about even" when the chart shows you're down 12% over the last three weeks. That honesty is what separates recreational bettors from people who actually build wealth through sports betting.
Bankroll tracking also reveals patterns you'd never notice otherwise. Maybe you crush NBA totals but hemorrhage money on NFL sides. Maybe your Tuesday bets are significantly more profitable than your weekend action. You won't know any of this unless you're writing it down. And once you know, you can adjust your Kelly fractions accordingly, betting more aggressively where your edge is strongest and cutting back where it's thin. If you're new to the concept, start with our simple Kelly Criterion guide before diving into tracking.
Every Sunday (or whatever day ends your betting week), calculate your total available betting funds. This is your new bankroll. Adjust all bet sizing accordingly.
Some bettors update daily, and if you have the discipline for that, go for it. But for most people, a weekly cadence hits the sweet spot. It's frequent enough to keep your bet sizes accurate and infrequent enough that you're not micromanaging every fluctuation. Pick a consistent day and stick to it. The key is that your "bankroll" number is always current when you're sizing your next bet.
When you sit down to update, add up everything: the cash in your sportsbook accounts, any pending bets that have already been graded but not settled, and any funds you've set aside specifically for betting. Don't include pending wagers that haven't been decided yet. Those are at risk and shouldn't factor into your available capital until they resolve.
| Week | Starting Bankroll | Win/Loss | New Bankroll | 5% Bet Size |
|---|---|---|---|---|
| Week 1 | $5,000 | +$300 | $5,300 | $265 |
| Week 2 | $5,300 | -$150 | $5,150 | $258 |
| Week 3 | $5,150 | +$400 | $5,550 | $278 |
| Week 4 | $5,550 | +$200 | $5,750 | $288 |
Notice how the bet size recalculates every week. In Week 1, 5% of $5,000 is $250, but after a $300 profit, 5% of $5,300 is $265. That extra $15 per bet doesn't seem like much, but over hundreds of bets across a full season, that compounding effect is enormous. It's also working in your favor during downswings. When the bankroll dropped to $5,150 in Week 2, the bet size dropped to $258, automatically reducing your exposure when things aren't going well.
You don't need fancy software for this. A basic spreadsheet with five or six columns does the job. Here's what to include in each row:
Date: When the bet was placed or the week ended. This creates your timeline and lets you spot trends over weeks and months.
Starting Bankroll: Your total available funds at the beginning of the period. This is the number your Kelly percentage multiplies against.
Bet Details: What you wagered on, the odds, and the Kelly fraction you used. This is optional for a simple tracker, but incredibly useful for analyzing your results later.
Win/Loss Amount: The net result for that period. Keep this as a raw dollar figure so you can see the actual impact on your bankroll.
New Bankroll: Starting bankroll plus or minus your win/loss. This becomes next period's starting bankroll.
Kelly Bet Size: Your chosen Kelly fraction multiplied by the new bankroll. If you're using half Kelly at 2.5%, and your new bankroll is $5,550, your next standard bet is $139. Write it down so you don't have to recalculate in the moment.
Keep this spreadsheet updated religiously. The bettors who track meticulously are the ones who survive long enough for their edge to compound. The ones who wing it are the ones posting "I used to have a bankroll" stories on Reddit.
Tracking your bankroll week to week is the bare minimum. If you want to actually improve as a bettor, there are a handful of metrics you should be reviewing at least once a month.
ROI (Return on Investment): Your total profit divided by your total amount wagered. This is the single most important number in your entire tracking system. If your ROI is positive, your edge is real. If it's negative over a meaningful sample size (200+ bets), something needs to change. For context, a 3-5% ROI over a full season is considered sharp. Anything above 8-10% is exceptional and probably unsustainable.
Win Rate by Sport or Bet Type: Break your results down by category. You might be +15% on NBA player props but -8% on NFL spreads. Kelly works best when you know where your edge actually lives, because you can allocate larger Kelly fractions to your strongest categories and use smaller fractions (or skip entirely) where the data says you're not profitable.
Drawdown History: A drawdown is the percentage decline from your bankroll's peak to its lowest point before recovering. If your bankroll hit $6,000 and then dropped to $4,800 before climbing back, that's a 20% drawdown. Track your maximum drawdown over time. If it keeps getting larger, you may be betting too aggressively. Most professionals keep their maximum drawdown under 20-25%. If yours is regularly exceeding 30%, consider moving from half Kelly to quarter Kelly. The bankroll simulator can help you stress-test different fraction sizes before committing real money.
Bankroll Growth Rate: Plot your bankroll on a simple line chart over time. A healthy Kelly approach produces a line that trends upward with occasional dips. If your chart looks like a heart monitor with violent swings in both directions, your bet sizing might be too aggressive relative to your actual edge. Steady, boring growth is the goal.
Only money you can afford to lose. Not rent. Not emergency funds. Not money you'll need next month. Your betting bankroll is completely separate from your living expenses.
This is not just a disclaimer. It's a structural requirement for Kelly to work properly. The Kelly formula assumes you can withstand losing streaks without needing to withdraw funds for bills. The moment you pull money out of your bankroll to cover rent, you've broken the system. Your bet sizes are now based on a number that's larger than what you actually have, and you're effectively over-betting every single wager.
A good rule of thumb: if losing your entire bankroll tomorrow would cause you financial stress, it's too large. Scale it down to a number that, if it vanished overnight, would be annoying but not devastating. That's your real bankroll. For a deeper breakdown of how to set this up properly, see our bankroll management guide.
If Kelly says bet 4% and you're using half Kelly, that's 2% of your current bankroll. If your bankroll is $6,000, your bet is $120. Recalculate this every week as your bankroll changes.
Here's a practical example that walks through the full workflow. Say you've identified value on an NBA moneyline at +150. You estimate the team's true probability of winning is 45%, but the implied odds from the book are only 40%. You plug those numbers into the Kelly Criterion formula and it spits out a recommended bet of 7.5% of your bankroll. That feels aggressive, and it should, because full Kelly is volatile. So you use half Kelly: 3.75% of your current bankroll.
If your bankroll was $5,550 this week, that's $208. You place the bet, it wins, and you collect $312 in profit (your $208 stake times 1.5). Your new bankroll is $5,862. Next week, when you run the same calculation on a similar opportunity, 3.75% is now $220 instead of $208. Your bet grew because your bankroll grew. That's the compounding engine at work.
Your tracking spreadsheet isn't just a record. It's an early warning system. Here are the signals that should trigger a change in your strategy.
Three consecutive weeks of losses: This doesn't necessarily mean your edge has disappeared, but it does mean you should temporarily reduce your Kelly fraction. Drop from half Kelly to quarter Kelly until the losing streak ends. Variance is real, and surviving it is more important than maximizing growth during it. Read more about common Kelly Criterion mistakes to avoid compounding the problem.
Drawdown exceeding 25%: If your bankroll has dropped more than 25% from its peak, pause and review everything. Are your probability estimates still accurate? Have the markets adjusted to something you were exploiting? Is your sample size large enough to be meaningful, or are you just running bad? Don't keep betting the same way and hoping things turn around. The data is telling you something.
Consistent positive ROI above 5%: This is the good scenario, but it still requires action. If you've been profitable over 300+ bets with a healthy ROI, you might consider gradually increasing your Kelly fraction. Moving from quarter Kelly to half Kelly over time, as your confidence in your edge grows, is the smart way to scale up. Don't jump from cautious to aggressive overnight.
Bankroll doubles: When your bankroll hits twice its starting value, consider withdrawing your original stake and continuing with "house money." This locks in your initial investment and removes the psychological pressure of losing money you started with. Your Kelly percentages continue to work the same way on the remaining bankroll, but the stress level drops significantly. For more on the psychology of bet sizing discipline, we've got a full breakdown.
Pro tip: Most profitable bettors grow their bankroll slowly. A 10-15% increase over a full season is excellent. If you're up 50% in two months, you're either getting lucky or taking too much risk. Slow and steady wins. The bettors who last decades in this game are the ones who treat a 12% annual return like a victory, because it is one. Compounded over five years, that 12% turns your bankroll into nearly double its starting value, and that's without taking unnecessary risks.
You don't need to build the perfect spreadsheet before you start. Open a Google Sheet, create five columns (Date, Starting Bankroll, Win/Loss, New Bankroll, Next Bet Size), and fill in today's numbers. That's it. You can add more columns and metrics later as you get comfortable with the process. The important thing is to start now and be consistent.
Kelly Criterion bankroll tracking is not complicated. It's just disciplined. Update your numbers every week, review your metrics every month, and let the math do the heavy lifting. Over time, your spreadsheet becomes the most valuable tool in your entire betting operation, more useful than any tout service, any tip sheet, any model. Because it tells you the truth about your own performance, and that truth is what lets you improve.