Market Math Tutorial

How to answer every drill in the trainer quickly and consistently.

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Input Rules

Type only the number. Do not type dollar signs, percent signs, commas, or a trailing c. For signed answers, include the minus sign if the value is negative.

Accepted

7, -4, 12.5, 3.25

Do not type units

Use 4.25, not $4.25. Use 55, not 55%.

Correct answers advance automatically. Press Enter when you want to mark an answer and see the calculation.

Edge

Edge means how many cents better your fair value is than the market price for the side you are buying.

YES edge = fair YES % - YES price
NO edge = fair NO % - NO price = (100 - fair YES %) - NO price
YES example

Prompt: YES 42c, fair YES 51%. Answer: 9, because 51 - 42 = 9.

NO example

Prompt: NO 38c, fair YES 55%. Fair NO is 45. Answer: 7, because 45 - 38 = 7.

Profit

Profit drills include payout profit, exit profit, and implied YES probability.

Resolution profit

Profit if correct = contracts x (100 - entry price) / 100
Example

Buy 50 YES at 40c. Profit if YES wins is 50 x 60c = $30. Answer: 30.

Exit profit

Exit profit = contracts x (sell price - buy price) / 100
Example

100 shares: buy 42c, sell 55c. Profit is 100 x 13c = $13. Answer: 13.

Implied probability

YES price implies YES probability directly. NO price implies YES probability = 100 - NO price.
Example

NO at 62c implies YES at 38%. Answer: 38.

EV

Expected value before fees is edge multiplied by position size.

EV dollars = contracts x (fair side cents - price cents) / 100
YES example

100 YES at 45c, fair YES 52%. Edge is 7c. EV is 100 x 7c = $7. Answer: 7.

Negative EV example

50 YES at 60c, fair YES 54%. Edge is -6c. EV is 50 x -6c = -$3. Answer: -3.

Kelly

The trainer asks for full Kelly bankroll percent on a YES trade.

Full Kelly % = 100 x edge cents / profit-if-correct cents
For YES: edge = fair - price, profit-if-correct = 100 - price
Example

YES 40c, fair 52%. Edge is 12c. Profit-if-correct is 60c. Kelly is 12 / 60 = 20%. Answer: 20.

This is full Kelly, not half Kelly or quarter Kelly. In real trading you may size smaller for model risk and correlation.

Fees

Fee drills use the standard prediction-market curve shape: fee coefficient times contracts times p x (1-p), where p is price as a decimal.

Fee or rebate = coefficient x contracts x price_decimal x (1 - price_decimal)
  • Kalshi taker coefficient: 0.07, rounded up to the next cent.
  • Kalshi maker coefficient: 0.0175, rounded up to the next cent.
  • Polymarket taker coefficient: 0.05, rounded to nearest cent with banker's rounding.
  • Polymarket maker coefficient: 0.0125, rounded to nearest cent with banker's rounding.
Example

Kalshi taker: 100 contracts at 50c. Raw fee is 0.07 x 100 x 0.50 x 0.50 = 1.75. Answer: 1.75.

Mental shortcut

The fee is largest near 50c and smaller near the tails. At 50c, p x (1-p) = 0.25.

Arb

Arbitrage drills use complete YES+NO sets. One complete set pays $1 no matter which side wins.

Profit per set = 100c - YES price - NO price
Complete sets = min(YES size, NO size)
Total locked profit = complete sets x profit per set / 100
Per-set example

YES 44c, NO 53c. Cost is 97c. Profit per complete set is 3c. Answer: 3.

Total example

YES 44c x100, NO 53c x75. You can make 75 complete sets. Profit is 75 x 3c = $2.25. Answer: 2.25.

Break

Breakeven drills ask for the minimum fair YES probability after taker fees. Think of this as price plus fee per contract.

Breakeven fair % = entry price cents + fee cents per contract
Fee cents per contract = total fee dollars / contracts x 100
Example

Buy YES 40c x100 with a $1.68 fee. Fee per contract is $1.68 / 100 = 1.68c. Breakeven fair is 41.7% after rounding to one decimal. Answer: 41.7.

Size

Size drills ask how many whole contracts fit in a dollar budget before fees.

Contracts = floor(budget dollars / price dollars)
Example

$50 budget, YES at 40c. Each contract costs $0.40. 50 / 0.40 = 125. Answer: 125.

Always round down. You cannot buy a fractional contract in this drill.

Mix / Weak

Mix randomly samples every drill type. Use it when you want broad practice.

Weak chooses the drill type where your local accuracy is lowest after you have attempted enough examples. The Focus panel shows what it currently thinks your weakest area is.

Practice loop

Use Mix for a timed round, then switch to Weak for untimed cleanup. When your weak area changes, the trainer will start targeting the next bottleneck.