The Mathematics of the Consistency Rule: A Trader's Formula for Staying Compliant

Most prop firm traders understand the consistency rule conceptually: no single day should dominate your profits. Fewer traders understand the actual math well enough to calculate, in real time, how much they can make today without triggering a violation — or how many additional trading days they need to "dilute" an outsized session that already happened.

The formula is simple. What you do with it is what matters.

The Core Formula

A trader's daily profit P_d must satisfy:

P_d ≤ C × P_total

Where:

• P_d = profit from any single trading day
• C = the consistency threshold (e.g., 0.30 for 30%, 0.40 for 40%, 0.50 for 50%)
• P_total = your total cumulative profit over the evaluation or payout cycle

In practical terms: your best single day's profit, divided by your total profit, must be less than or equal to the consistency threshold.

Example 1: Checking Whether You're Compliant

Firm uses a 40% consistency rule. Your evaluation results:

• Day 1: +$800
• Day 2: +$1,400
• Day 3: +$600
• Day 4: +$200
• Total: +$3,000 (profit target met)

Best single day: $1,400 (Day 2).
Consistency check: $1,400 ÷ $3,000 = 46.7%

46.7% > 40%. Consistency rule violated despite hitting the profit target.

Example 2: How Much Can You Make Today?

Before entering a session, you can calculate your maximum compliant daily profit given your current cumulative P&L.

Formula for today's ceiling:

Max P_d = C × P_total

But P_total includes today's profit — so this is slightly circular. The practical working formula:

Max P_d = (C × P_prior) ÷ (1 - C)

Where P_prior is your cumulative profit before today's session.

Example: You have $2,000 in cumulative profit. The firm uses a 40% consistency rule. How much can you make today?

Max P_d = (0.40 × $2,000) ÷ (1 - 0.40) = $800 ÷ 0.60 = $1,333

If you make more than $1,333 today, today's session will represent more than 40% of your updated cumulative total. You'd need to continue trading (adding more days) to bring the ratio back into compliance.

Example 3: Diluting an Oversized Day

You had a monster session — $2,000 in one day. Your prior cumulative was $1,500. Total is now $3,500. But $2,000 ÷ $3,500 = 57%. You're using a 50% rule. Violation — unless you add more trading days.

How much more do you need to earn to bring it into compliance?

You need: $2,000 ≤ 0.50 × P_total
Which means: P_total ≥ $2,000 ÷ 0.50 = $4,000

You currently have $3,500. You need $500 more in net profit (on additional trading days) to dilute the big session to 50% of the total. Add those days, and you're compliant.

This is exactly what most firms mean when they say "continue trading until the rule is met" rather than voiding your evaluation — the math just needs time to normalize.

Consistency Thresholds by Firm (2026)

Automating Compliance with Contract Sizing

The mechanical approach to consistency rule compliance — calculate the ceiling before each session and size positions so you can't exceed it — is manageable for one account. Across five or ten accounts with different cumulative profit levels, the per-account calculations become unwieldy.

Copilink's risk management layer tracks per-account cumulative profit and monitors daily contribution percentage in real time. As you approach a consistency threshold on any individual account, it alerts you — and can dynamically adjust contract sizing on that account to ensure no single session exceeds the configured threshold. The math runs automatically, per account, so you're not managing spreadsheets while managing live trades.

Learn more about setting up consistency rule automation across multiple funded accounts at copilink.com.