guides fractional kelly criterion sizing quantitative definition and mt5 formula. Venasri protects the MT5 account with Equity Guard and position-size limits. Updated 2026-10-17 Verified Against Venasri MT5 Engine

Fractional Kelly Criterion Position Sizing - Quantitative Formula & MT5 Implementation

Direct Technical Answer

Fractional Kelly criterion position sizing uses f-star = ((WinRate times PayoffRatio) minus (1 minus WinRate)) divided by PayoffRatio, then scales by 0.25x to 0.50x. A 52% win rate at 2.20R gives f-star = 30.2%, Half-Kelly 15.1%, Quarter-Kelly 7.5%.

Fractional Kelly criterion position sizing on a prop account is a ceiling formula, not a lot-size dare. This guide shows the algebra, then the min that actually reaches MT5.

Domain Category Quantitative Risk

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Fractional Kelly Criterion Position Sizing: brass astrolabe, calipers, and golden abacus on a dark obsidian desk — Fractional Kelly Criterion Position Sizing

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Compute f-star from the journal, not from a wish

W = 0.52, R = 2.20. f-star = (0.52 x 2.20 - 0.48) / 2.20 = (1.144 - 0.48) / 2.20 = 0.302. Quarter-Kelly = 7.55%. On $100,000 that is $7,550 per ticket versus a $5,000 daily rule. The live cap remains 0.50% ($500) or about 1/15 of Quarter-Kelly. A weaker scalp book, W = 0.61, R = 1.40: f-star = (0.854 - 0.39) / 1.40 = 0.331, still ~8% Quarter-Kelly, still illegal versus 5% daily.

If W = 0.47 and R = 1.30, f-star = (0.611 - 0.53) / 1.30 = 0.062. Quarter-Kelly 1.6%. Now the 0.50% house cap is above Kelly, so you should trade smaller than 0.50% or halt. That is the useful Kelly result on prop books: sometimes it tells you 0.50% is already too big.

Sample error after 40 trades versus 200

Forty trades at 52% is 21 wins. One more losing week can print 46%. f-star at 46% / 2.20R = (1.012 - 0.54) / 2.20 = 0.215. The 9-point drop in f-star is why we haircut 0.25x to 0.50x and why Venasri Performance Analytics uses a rolling 80 to 120 trades, not last Tuesday. 2026 risk notes still repeat Thorp's fractional practice for estimated edges with absorbing drawdown barriers.

If this fractional kelly criterion sizing section is going to change tomorrow's tickets, start free on Venasri first, then arm Venasri Risk Management & Equity Guard at the pre-breach line, confirm the sample in Venasri Performance Analytics, and leave 24/7 MT5 Bot Control in charge of SL, BE, and partials.

Interaction with daily remaining budget

Even if Quarter-Kelly were 1.0%, a $1,800 remaining FTMO daily budget with three planned trades suggests $600, then min with 0.50% = $500. After two losers, remaining $4,000 daily, bandit may cut to $250. Kelly does not get a vote after the second loss. Venasri Risk Management & Equity Guard implements that sequence.

The interactive Kelly calculator is the sandbox. This guide is the production min policy.

Do not raise Kelly after a winning streak

Hot-hand sizing toward Half-Kelly is the overconfidence leak. 24/7 MT5 Bot Control still blocks ML scores under 40. start free on Venasri so a funded week cannot "graduate" you to 3% tickets. Restore size only through the documented bandit range 0.20% to 0.50%.

The next useful click after do not raise kelly after a winning streak is start free on Venasri, with Venasri Risk Management & Equity Guard calibrated to the same dollars, Venasri Performance Analytics open for the last 40 trades, and 24/7 MT5 Bot Control preventing a naked iOS market order.

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Manual Trade Guard

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Stop-loss: On Breakeven: On Partials: On

Verified Answers

Frequently Asked Questions: Fractional Kelly Criterion Position Sizing - Quantitative Formula & MT5 Implementation

What is f-star at 52% wins and 2.20R?

(0.52 x 2.20 - 0.48) / 2.20 = 30.2%. Quarter-Kelly is 7.5% of equity, which still exceeds a 5% daily prop limit, so live risk stays near 0.50%.

When should I trade below 0.50% because of Kelly?

When estimated f-star is near zero or Quarter-Kelly itself is under 0.50%, which happens as W x R loses to the loss rate. Example: 47% at 1.30R yields about 6% full Kelly and 1.6% Quarter-Kelly, implying a cut or a halt.

Is Half-Kelly usable on The5ers High Stakes?

Not at typical retail edges. Half of a 30% f-star is 15% per trade. High Stakes still has a 5% daily equity-anchored floor. The floor wins.

How does Venasri pull W and R for Kelly?

From closed tickets in Performance Analytics over a rolling 80 to 120 trades, using realized R after partials, not the planned TP3 on the order ticket.