---
title: "Calculation window"
description: "The calculation window is how many months of past data an allocation method reads when it computes weights — the lookback behind volatility and ranking."
canonical_url: "https://fincanva.com/glossary/calculation-window"
last_updated: "2026-10-06"
md_url: "https://fincanva.com/glossary/calculation-window.md"
---

# Calculation window

The calculation window is how many months of past data an [allocation method](/glossary/allocation-and-allocation-method) reads when it computes weights — the lookback that feeds its volatility, correlation, [beta](/glossary/beta) and ranking calculations at each [rebalance](/glossary/rebalance). History older than the window has no influence on the weights. In the [strategy](/glossary/strategy) editor the field is labelled **In-sample**.

**Also seen as:** In-sample, lookback, lookback window, in-sample period, estimation window

## How does Fincanva handle it?

- The default is **12 months**. The field takes whole months with a minimum of 1 — limited to the seven values above for the methods that read annualised volatility — and the unit shown beside it is "mo".
- The window belongs to the allocation profile, so a strategy that has a Risk-Off allocation can read one window in Risk-On and a different one in Risk-Off.
- [Beta neutral](/glossary/beta-neutral) carries a second, separate window — its **Ranking calculation window** — for the metric it ranks on, while the profile's calculation window controls its beta estimation. The app spells the split out: "How far back the ranking metric reads — distinct from the Calculation window above, which controls the beta-estimation window."
- Changing the window changes a strategy's inputs, so the [backtest](/glossary/backtest) has to be run again before the results reflect it.

## What does the calculation window change?

The calculation window changes the weights a method produces without changing the method itself, because it changes the span of history the method measures over. The app's own note reads: "Historical window used by the active method for volatility, correlation, beta, and similar calculations. Default 12." A short window makes the weights react quickly to recent conditions and shift noticeably from one rebalance to the next; a long window averages across more market regimes and produces steadier weights that respond slowly. Neither is more correct than the other — they answer different questions about the same instruments.

The window is measured backwards from each rebalance date *inside* the backtest, not from today, so a method using a 12-month window at a rebalance in March 2015 reads 2014–2015 data, not recent data.

## Which allocation methods read the calculation window?

| Reads the window | Ignores the window |
|---|---|
| Inverse volatility · [Risk parity](/glossary/risk-parity) · [MPT (Markowitz)](/glossary/mpt-markowitz) · [Min correlation](/glossary/min-correlation) · [Mimicking](/glossary/mimicking) · Beta neutral · [Max diversification](/glossary/max-diversification) · [HRP](/glossary/hierarchical-risk-parity) · [HERC](/glossary/hierarchical-equal-risk-contribution) · [NCO](/glossary/nested-clustered-optimization) · [Min MAD](/glossary/min-mad) · [Min CVaR and Scenario CVaR](/glossary/min-cvar) · [CDaR](/glossary/conditional-drawdown-at-risk) · [EVaR](/glossary/entropic-value-at-risk) · [Robust worst case](/glossary/robust-worst-case) · [Stochastic programming](/glossary/stochastic-programming) | [Equal weights](/glossary/equal-weights) · [Fixed weights](/glossary/fixed-weights) · [Floating](/glossary/floating) · [Market cap](/glossary/market-cap) |

[Ranking-based](/glossary/ranking-based) is the conditional case: it reads the window when its ranking metric is [Price Change](/glossary/percent-change), Volatility or [Sharpe ratio](/glossary/sharpe-ratio), and ignores it for [Average Momentum](/glossary/average-momentum) and P/E Ratio. When the active method does not read the window, the **In-sample** field is not displayed at all — there is nothing for it to set.

## Which window lengths can you choose?

A method that reads annualised [volatility](/glossary/volatility) over the window accepts only **1, 2, 3, 6, 12, 18 or 24 months**; every other method takes any whole number of months from 1 upward. The seven-value case covers:

- [Inverse volatility](/glossary/inverse-volatility) with the risk measure **Annualized volatility**, in a strategy and in a [Combined](/glossary/combined);
- [Min correlation](/glossary/min-correlation), always;
- [Ranking-based](/glossary/ranking-based) with the ranking metric **Volatility**, in a strategy and in a Combined;
- [Beta neutral](/glossary/beta-neutral) ranked by **Volatility**, for its **Ranking window**.

For those methods the field is a menu of the seven values rather than a number you type. A strategy saved earlier with another value still opens and still saves — the menu shows that value as the current, greyed-out item — but its backtest does not start: the [strategy alert](/glossary/strategy-alerts) "The strategy does not run with this in-sample period" blocks it until you pick one of the seven. On a strategy holding a single picked [instrument](/glossary/instrument), Inverse volatility and Min correlation have nothing to weigh and never read the window, so the alert stays silent there.

## What does it look like in practice?

A strategy holds five ETFs and uses [Inverse volatility](/glossary/inverse-volatility), which gives each holding a weight inversely proportional to its risk. With the calculation window at 6 months, the weights are set from the last six months of returns: an ETF that was turbulent through that half-year but calm before it measures as high-risk and receives a small weight. Change the window to 24 and that same turbulent half-year is averaged against eighteen quieter months, so its measured [volatility](/glossary/volatility) falls and its weight rises. Same method, same five ETFs, same rebalance date — a different allocation, purely because the method was shown a different span of history.

Fincanva is for education and illustration only. It is not personalised financial advice, and past or simulated results do not predict future ones. [Read the Terms Addendum](https://fincanva.com/terms/addendum#section-3)