Teacher's Bet: Sports Betting Math, De-Vig, +EV, Kelly

Figure	Fair line	FanDuelas of 4:02 PM	Kalshi✓ live	DraftKings
Bills	-13156.7%	-15861.2%	-13757.8%	-14659.3%
EV	0.00%	-7.40%	-1.90%	-4.45%
Chiefs	+13143.3%	+13642.4%	+13243.1%	+11746.1%
EV	0.00%	+2.16%	+0.43%	-6.06%
Vig	0.00%	3.61%	0.91%	5.43%

The board

Find the edges.

Every venue’s price side by side, measured against a consensus fair line pooled across every venue that qualifies. Best price checked. Stale lines flagged with the time the venue last moved.

Prices we read

We look at top US books and the Kalshi exchange market for statistical outliers.

fair line+100+120−105+145−130+100

+104+114+110+4−62−116+11+88+151+16−64−132−20+49+70+104

▲ +EV 2.0%−4.5%−4.6%▲ +EV 2.4%−0.7%▲ +EV 2.0%

+99+115+118+15−49−101+10+78+133+1−78−145−29+42+64+99

−0.5%−0.9%▲ +EV 1.9%−4.9%−4.5%−0.5%

+91+115+125+16−52−107+12+85+144+18−58−122−22+41+60+91

−4.5%▲ +EV 2.3%−0.9%−0.4%▲ +EV 2.9%−4.5%

Illustration, not a live quote.

Every price, side by side

The best price on each side is checked. A venue that has not moved in a while is dimmed, with the time it last did. Nothing here is more certain than its timestamp, so the timestamp is always shown.

Fair value, derived

The venue’s cut is stripped out, then the price is measured against a consensus line pooled across every qualifying venue. When a venue pays above fair, you see how much, and why.

Sizing you can interrogate

Half Kelly by default, quarter if you prefer, every step replayable. When a game holds no edge it says $0. Plenty do. Finding the ones that don’t is the whole job.

Show your work

A Tale of Two Bettors

It was the best of odds, it was the worst of odds. $5,000 each, 1,000 bets, one season.

Average Joe

Takes the coin flip at −110.
$250 flat, every time.

+EV Evan

Only takes +2% to +4% EV.
Half Kelly, every time.

Joe’s $250 is worth −$11.36 the moment he places it. Evan stakes 1.1–2.2% of what is left. Assumptions, not a promise.

One season proves nothing. Here are a million.

Nobody can tell you how your season ends. A staking rule moves the shape of the outcomes, and a shape is checkable.

The calculators

Nineteen of them. No signup.

The de-vig, Kelly and arbitrage math behind them is published as an MIT-licensed Python library, so any number here can be reproduced without asking permission.

no-vig fair odds

Odds, side A−150 Odds, side B+130 De-vig methodProportionalPowerShin ▾

implied 60.0% + 43.5% = 103.5%

100

over by 3.5%: the vig, the book’s cut

fair: 58.0%58.4%58.3% / 42.0%41.6%41.7% · fair price −138−140−140 / +138+140+140

The no-vig calculator, on a loop: proportional, then power, then Shin, each with its own answer. The real one runs in your browser: every step shown, free, no signup.

No-vigstrips the venue’s cut out of a two-way price Expected valuea posted price against your own probability Kellythe stake an edge supports, half or quarter Arbitragewhether two prices sum under 100%, then the split Closing line valueyour price against the number the market closed at Parlaycombined odds, payout, and how the vig compounds Free betwhat a bonus token converts to in cash Kalshi feesthe taker fee, and the break-even it moves you to

All nineteen calculators · the free Learn course behind them

The Learn course

Welcome to class.

Learn sports betting math, step by step, from the adorable class hamsters Pip and Chalk.

PipWins half the time. Everyone likes him more.

ChalkAlso wins half the time.

Average Joe, Bookie Brian and +EV Evan at the rail. Illustration, not a live quote.

Start the free course

The Report Card

Log the bet. Take the grade.

Tap a price and it goes on your card, graded on closing line value when the market closes. Wins and losses move your bankroll. The term gets a GPA.

Term Reportsample

Bills −110 · DraftKings stake $110 · closed 53.7% · CLV +1.3 W +$100A

Cowboys +145 · FanDuel stake $40 · closed 42.6% · CLV +1.8 L −$40A

Jets +136 · Kalshi stake $50 · closed 42.8% · CLV +0.4 W +$68B

4.004.003.67 term GPA · record 2–1 bankroll $1,000 → $1,128 = (4.0 + 4.0 + 3.0) / 3

Sample numbers, worked end to end. Free grades one bet at a time; an Extra Credit account keeps the whole term, on every device.

One tap logs it. Tap a price on the board and it lands here, timestamped, with the stake on record.
Graded on closing line value. Your price against where the market closed, in probability points. Beat the close and the worst you can grade is a B.
Wins, losses and the bankroll. Set a start once. Settled bets move it; open bets print as exposure, not wishful thinking.
A live term GPA. The plain mean of your grade points, arithmetic shown, like every other number here.
Compare with your friends. One tap draws the card as a photo for the group chat. The math is ours; the bragging is on you.

The price

Everyone gets the same math. Some people just get it sooner.

Free

$0No account, no email, no card.

Every calculator, with every step shown
The whole Learn course. Free
The board, on a two-hour delay
The Report Card, one bet at a time
Real-time Kalshi board
Live board, all sports & props
+EV / Arbitrage alerts
Hedge watch on your logged bets
Your Report Card saved, exportable
The data API: the live board and alerts as JSON
Discord alert channels

Start free

founder rate · first 100 subscribers

Extra Credit

$25/mofor your first 12 months, then $39/mo

Everything in Free
Real-time Kalshi board
Live board, all sports & props
+EV / Arbitrage alerts
Hedge watch on your logged bets
Your Report Card saved, exportable
The data API: the live board and alerts as JSON
The Discord alert channels

Pricing and the full terms →

Full terms

The board is pregame: a game leaves the board at kickoff, and alerts are pregame too.

Teacher’s Bet is an analytics tool for informational and entertainment purposes only. It does not accept wagers, hold funds, facilitate bet placement, or give betting advice. All outputs are calculations on user-supplied inputs. No feature of any tier guarantees any outcome.

The receipts

Don’t trust our math? Check it yourself.

Every result has a show-the-work path. The methods are documented in plain language. The math library itself is public source code.

Formulas Methodology Open source API docs Editorial policy

Raised hands

Sports betting analytics: fair questions

Do you have a free trial?

Yes. You earn it: finish the ten free Learn modules, about an hour of reading, and your first month of Extra Credit is free. Stripe asks for a card, it is one per account, and it continues at $39 a month unless you cancel. Cancel is one click.

Do you sell picks?

No. Teacher's Bet never says "bet this." Every output is arithmetic on your inputs or posted odds, with the benchmark, method, and timestamps shown. You decide what that's worth.

What sports are on the board?

NFL, NBA, WNBA, NHL, MLB, college football, college basketball, boxing and MMA, plus player props. Football leads; the rest follow the season's calendar.

Can Teacher's Bet guarantee profit?

No, and be suspicious of anything that says it can. Even arbitrage carries real execution risk, and the tool says so every time it flags one.

Where do the odds come from?

Licensed APIs, never scraping: the Kalshi exchange API for prediction markets, and a commercial odds API for the sportsbooks. Every quote carries two timestamps: when we pulled it, and when the venue last moved it. The exchange feed streams sub-second from the Kalshi order book; the free board shows everything two hours behind.

Why should I trust the math?

You don't have to. You can check it. Every result has a "Show the work" button, the methods are documented in plain language on the Learn page, and the math library itself is public source code.

Is there an iPhone app?

We submitted it to the App Store in August and expect it soon. The review queue is not ours to schedule, so that is what we are working to rather than a promise. Until it lands, Safari’s Share menu adds the web app to your Home Screen in about twenty seconds, full screen, alerts included. Steps on the install page.

Smarter betting?We do the math.You do the rest.