# Rolling Forecast Builder

> Blends actuals-to-date with a forward forecast via a bundled calculator, bridges the result against the original plan, and flags when the forecast's implied run rate jumps well above what's actually been achieved so far without a named reason. Use whenever the user needs an updated full-year view partway through the year, wants a rolling or continuous forecast rather than a once-a-year budget, or has a re-forecast where the remaining months quietly assume a faster pace than the actuals have shown with no explanation.

- Skill: `natan-mohart/rolling-forecast-builder` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add natan-mohart/rolling-forecast-builder`
- Raw SKILL.md: https://api.skillmd.com/api/skills/natan-mohart/rolling-forecast-builder/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Finance & Business
- Author: Natan-Mohart (https://skillmd.com/u/natan-mohart)
- Updated: 2026-09-21
- Page: https://skillmd.com/skills/natan-mohart/rolling-forecast-builder

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# Rolling Forecast Builder

## When to use
Use whenever the year is partway through and the full-year view needs updating with real actuals, replacing a forecast that either ignores actuals entirely (still showing the original budget) or quietly assumes an accelerating pace for the remaining months with no stated reason.

## What it does
Blends actual results for completed months with a forecast for remaining months via a bundled calculator, computes the resulting full-year view, bridges it against the original plan, and explicitly flags when the forecast run rate for remaining months is meaningfully higher than the actual run rate achieved so far — the most common way rolling forecasts quietly turn optimistic without anyone noticing.

## Method
1. **Pull actuals for every completed month**, not an estimate — the forecast is only as trustworthy as the actuals it's anchored to.
2. **Build the forecast for remaining months from real drivers**, using the same driver-based-budget-builder discipline, updated with anything learned from the actuals so far (a channel that's underperforming, a cost that's running higher than planned).
3. **Run the bundled calculator** (`scripts/rolling_forecast.py`) to get the full monthly view (actual and forecast months together), the resulting full-year total, and the bridge against the original annual plan.
4. **Read the run-rate comparison explicitly.** If the forecast's monthly run rate for remaining months is more than 15% above the actual run rate achieved in completed months, that's a flag worth resolving before the forecast goes out — either there's a specific, named reason (a signed deal, a seasonal pattern, a planned launch) or the forecast is quietly assuming things get better with no basis.
5. **State the bridge to plan in both dollars and percentage**, and be explicit about whether the business is tracking ahead, on, or behind the original commitment — a rolling forecast's job is to catch a miss early, not to smooth it into invisibility.
6. **Update the forecast on a fixed cadence** (monthly or quarterly), not ad hoc — a rolling forecast that only gets refreshed when someone remembers to do it defeats its own purpose.
7. **Carry forward the reasons behind material changes** from one forecast cycle to the next, so a pattern of consistently over-optimistic remaining-month forecasts becomes visible over time, not just within a single cycle.

## Inputs
- Actual results by month for completed months
- Forecast for remaining months, built from updated drivers
- The original annual plan to bridge against
- Config saved as JSON matching the format documented at the top of `scripts/rolling_forecast.py`

## Output format
Month-by-month table of actuals and forecast with running cumulative total; full-year forecast total; bridge to original plan in dollars and percentage; actual vs. forecast monthly run-rate comparison with an explicit flag if the forecast assumes unexplained acceleration.

## Example
Five months of actuals average $1.9M per month; the forecast for the remaining seven months averages $2.24M, an 18% jump the calculator flags automatically. The team traces it to a genuinely signed enterprise deal starting month 7, a specific, defensible reason, so the forecast stands, but the flag forced that justification to be stated explicitly rather than the acceleration passing through unquestioned.

## Common pitfalls
- Forecasting remaining months at a faster pace than actuals have shown, with no specific driver behind the acceleration.
- Refreshing the forecast irregularly instead of on a fixed cadence, so it drifts out of date exactly when it matters most.
- Reporting the bridge to plan only in dollars or only in percentage, when both tell a different part of the story.