Vol-Targeted Position Sizer · Advanced
Free to readHow the Sizing Math Works
Realized vol, inverse-vol scaling, regime percentiles, and the Nations-index multiplier — the complete recipe behind the number the tool delivers.
The size the tool delivers is not a heuristic — it is the output of three computations applied in sequence. This page walks through each one exactly.
Step 1 — Realized volatility
The tool computes the underlying's realized volatility as the annualized standard deviation of daily log returns over a trailing window — by default the last 30 trading days, scaled by √252 to express it in annual terms. This is the same calculation as the Volatility Cones tool. The result is a single number: how much the underlying has actually moved, annualized, over the recent past.
Each realized-vol reading is the annualized standard deviation of the daily return series inside the trailing window. The √252 factor puts it in the same annual units as implied vol readings.
Step 2 — Inverse-vol position size
Given the realized vol σ and the user's per-position volatility target T (as a decimal, e.g., 0.01 for 1%), the full position notional is:
notional = capital × (T / σ)
If capital is $100,000, the target is 1%, and realized vol is 20%, the notional is $100,000 × (0.01 / 0.20) = $5,000 — a 5% allocation. If realized vol doubles to 40%, the notional halves to $2,500. That inverse relationship is the mechanism: higher vol → smaller notional → same expected risk contribution.
Step 3 — Realized-vol percentile
The tool measures the trailing-year realized-vol percentile — where today's 30-day realized vol sits in the distribution of all 30-day realized-vol readings over the past 252 trading days. A reading at the 92nd percentile means that only 8% of the trailing year saw realized vol this high. Percentile-in rather than level is what matters: a 20% realized vol at the 90th percentile signals a stressful regime; 20% at the 40th percentile signals a normal one — the number is the same, but the regime interpretation is different.
Step 4 — Regime classification and the multiplier
The tool combines three inputs to classify the regime: the realized-vol percentile, the current VolDex® 30-day implied vol, and the RiskDex® reading. The Nations indexes are live: VolDex® is the clean at-the-money implied vol at the 30-day tenor; RiskDex® measures the risk premium in the options market. Their combination distinguishes a market where realized vol is high but implied is catching up (genuine stress) from one where implied is already collapsing (stress subsiding).
The regime determines the multiplier. Calm conditions let the full inverse-vol size run; Stressed conditions cut gross exposure by more than half. The Nations indexes calibrate the boundaries in real time.
Step 5 — Shares
Converting notional to shares is the final step: shares = adjusted notional / current price. The tool pulls the live price and rounds to the nearest whole share (or lot, depending on the underlying). The share count, not the notional, is what you enter in your order ticket.
Rebalancing as vol changes
Vol-targeted sizing is not set-and-forget. As the underlying's realized vol changes — which it does, sometimes rapidly — the target notional changes with it. The tool is designed to be re-run periodically: at minimum, when the regime classification changes; ideally weekly for active positions. If a calm-regime position is still on when the regime flips to Stressed, the correct action is to trim to the new adjusted size, not wait for the position to do the trimming for you.
Vol-targeting equalizes the expected risk contribution of each position at the time of sizing. It cannot prevent gap risk — overnight or weekend moves that skip the target entirely. It also doesn't account for correlation: a book of ten equally-sized tech positions is not ten independent risks. And it is not a stop-loss: once a position is on, realized losses can exceed the vol-implied target if the market moves before a rebalance.
The methodology is free. To run the full calculation on live data: ETFs via ETF Analytics, single stocks via ETF + Equities. The Nations-index regime feed — VolDex® 30d, RiskDex®, and the full multiplier table — is included with Everything.
See plans →Your next step
Open the tool → Read: trading with vol-targeted sizing → Case study: sizing down in a stressed regime →Educational content from Nations Indexes. VolDex® and RiskDex® are registered marks of Nations Indexes. Realized-vol estimates carry known look-back dependence; figures are schematic. Nothing here is investment advice.