How I Built a Python Trading Risk Calculator in 200 Lines (No Libraries)

One of the biggest mistakes beginner traders make: entering trades without calculating their position size properly. They risk 20% of their capital on a single trade. Then they wonder why they blow their account in 3 weeks. So I built a simple Python script that does the math automatically. No pandas. No external libraries. Pure Python stdlib. Here is how it works. The Core Math of Position Sizing Before writing a single line of code, let us understand what we are calculating: Rule #1: Risk X% of capital per trade (professional standard: 1-2%) Rule #2: The position size is calculated from: how far your stop loss is from entry risk_amount = capital * (risk_pct / 100) position_value = (risk_amount * entry_price) / stop_loss_distance position_size_units = position_value / entry_price That is the core. If you only remember one thing from this article, remember this formula. Risk/Reward Ratio sl_distance = abs(entry - stop_loss) tp_distance = abs(take_profit - entry) rr_ratio = tp_distance