---
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/docs/strategies/calculation-window"
last_updated: "2026-07-25"
md_url: "https://fincanva.com/docs/strategies/calculation-window.md"
---

# Calculation window

The calculation window is how many months of past data an [allocation method](/docs/strategies/allocation-and-allocation-method) reads when it computes weights — the lookback that feeds its volatility, correlation, beta and ranking calculations at each [rebalance](/docs/backtesting/rebalance). It is a single number of months, set per allocation profile, and it bounds everything the method can see: history older than the window has no influence on the weights produced.

**Also seen as:** In-sample (the field label in the strategy editor), lookback, lookback window, in-sample period, estimation window

## 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 · [MPT (Markowitz)](/docs/strategies/modern-portfolio-theory) · [Min Correlation](/docs/strategies/min-correlation) · Mimicking · Beta Neutral | [Equal Weights](/docs/strategies/equal-weights) · [Fixed Allocation](/docs/strategies/fixed-weights) · Floating · [Market Cap](/docs/strategies/market-cap-weighted) |

[Ranking-Based](/docs/strategies/ranking-based) is the conditional case: it reads the window when its ranking metric is Price Change, Volatility or Sharpe Ratio, and ignores it for 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.

## Defaults in Fincanva

- The default is **12 months**. The field takes whole months with a minimum of 1 and no fixed ceiling; 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](/docs/strategies/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 has to be run again before the results reflect it.

## Worked example

A strategy holds five ETFs and uses [Inverse Volatility](/docs/strategies/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](/docs/analysis/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.