Analyst / planner

Simple forecast builder

Immediate result: A transparent forecast with method, formulas, base, high and low cases.

Problem it solvesTeams need a forecast by Friday and either guess or overbuild a model.

Download SKILL.md

Add this skill to

ChatGPT Claude Gemini Perplexity

You paste

Monthly orders Oct 2025–Sep 2026, forecast Oct–Dec 2026

You get

History: +3% a month, with a Diwali spike (Oct–Nov ≈ 1.4× normal).

Method: seasonal naive × trend — simple and explainable.

Base Nov 2026: 18,900 · low 16,800 · high 21,000

About this skill

About Simple forecast builder

Teams that need a forecast by Friday either guess or build a model nobody understands. This skill describes the trend and seasonality in your history, picks a simple, explainable method — moving average, growth rate or seasonal naive — and says why. It produces base, high and low forecasts with formulas you can paste into a spreadsheet, and lists the assumptions that would change the numbers most. It always gives a range, never a single certain figure, so the forecast can be planned around honestly. To use it, paste the skill into your assistant and send historical monthly numbers (at least 12 months ideally) and what you need to forecast.

Simple forecast builder AI skill for Analyst / planner: you paste "Monthly orders Oct 2025–Sep 2026, forecast Oct–Dec 2026" and get "History: +3% a month, with a Diwali spike (Oct–Nov ≈ 1.4× normal)." — Simple forecast builder — example input and the first lines it returns. Works in ChatGPT, Claude and Gemini.

Job profile: Data & analytics · Analyst / planner
Works in: ChatGPT, Claude, Gemini, Copilot, Claude Code
Format: Agent Skills (SKILL.md)
Price: Free, no sign-up

Install instructions

Copy, paste, send

1 Copy the skillPress Copy skill.
2 Paste it into a new chatChatGPT, Claude, Gemini or Copilot.
3 Send your inputSend historical monthly numbers (at least 12 months ideally) and what you need to forecast.

The skill — paste this into your AI assistant

# Skill: Simple forecast builder

You are running the "Simple forecast builder" skill for me. I work as: Analyst / planner. What I need from you: a transparent forecast with method, formulas, base, high and low cases.

## When I send you historical monthly numbers (at least 12 months ideally) and what I need to forecast
1. Describe the trend and seasonality in the history.
2. Pick a simple method (moving average, growth rate, seasonal naive) and say why.
3. Produce base, high and low forecasts with formulas you can paste into a spreadsheet.
4. List the assumptions that would change the forecast most.

## Reply in this format
- What the history shows
- Method
- Forecast table (base/high/low)
- Spreadsheet formulas
- Key assumptions

## Rules
- Never present a forecast as certain; always give a range.
- Use only the facts I give you; mark anything you had to assume with [ASSUMPTION].
- If something essential is missing, ask me one short question, then continue.
- No preamble or filler: start with the result.

Confirm you're ready in one line, then wait for me to send historical monthly numbers (at least 12 months ideally) and what I need to forecast.

Then sendHistorical monthly numbers (at least 12 months ideally) and what you need to forecast. For example: Monthly orders Oct 2025–Sep 2026, forecast Oct–Dec 2026

ChatGPT

Fastest: paste the skill as your first message in a new chat, then send your input.
To keep it: open a Project, choose Instructions (or Settings → Personalization → Custom instructions for every chat) and paste it there.
To share it with a team: create a custom GPT and paste the skill into its Instructions.
In the Codex app: copy the skill's folder into ~/.codex/skills/ (or Customize → Skills → Add → Create skill).

Claude

Fastest: paste the skill as your first message in a new chat, then send your input.
To keep it: create a Project, open Project instructions and paste the skill.
As a Claude Skill: download the skill's ZIP, then in Claude open Settings → Skills → Add → Upload skill and choose the file.

Gemini

Fastest: paste the skill as your first message in a new chat, then send your input.
To keep it: open Gems → New Gem, paste the skill into Instructions and save.

Microsoft Copilot

Fastest: paste the skill as your first message, then send your input.
In Microsoft 365 Copilot, save it as a prompt or paste it into an agent's instructions to reuse it.

Any other assistant

Paste the skill as the system prompt or first message in any chat assistant (Perplexity, Meta AI, DeepSeek, Mistral, local models).
Coding agents that read the Agent Skills format (SKILL.md) can load the downloaded file from their skills folder.

Install it permanently

Upload it to Claude, add it to ChatGPT's Codex app, clone it into Claude Code, or download the SKILL.md for any agent. Full guide with screenshots →

Download the ZIP and upload it in Claude. Claude then uses the skill on its own whenever a request matches.

Download ZIP

Quick setup

In Claude, open Settings → Skills (under Customize).
Click Add → Upload skill.
Choose the ZIP — don't unzip it — and make sure the skill is switched on.

Claude Settings with Skills selected under Customize, and the Add menu open showing Upload skill, Create a skill, Create with Claude and Record your screen

OpenAI's Codex app reads the same SKILL.md format. Copy the skill into your Codex skills folder:

Terminal

$ git -c http.version=HTTP/1.1 clone https://scienceofapps.com/skills/ai-skills.git
$ cp -r ai-skills/forecast-builder ~/.codex/skills/

Quick setup

Run the commands, then in Codex open Customize → Skills and press refresh.
No terminal? Click Add → Create skill and paste the skill.
Ask for the task — Codex loads the skill when the request matches.

The Codex app's Customize screen with Skills selected, listing installed skills, and the Add menu open showing Create skill and Record a skill

Clone the library and copy this skill into your Claude Code skills folder.

Terminal

$ git -c http.version=HTTP/1.1 clone https://scienceofapps.com/skills/ai-skills.git
$ cp -r ai-skills/forecast-builder ~/.claude/skills/

Quick setup

Run the two commands above (Git must be installed; no account needed).
Claude Code picks up skills in ~/.claude/skills/ for all projects, or .claude/skills/ inside one project.
Start a new session — Claude loads the skill when your request matches it.

Download the skill file and put it in a folder named after the skill.

Download SKILL.md

Quick setup

Claude Code: save it as ~/.claude/skills/forecast-builder/SKILL.md.
Claude apps: use the Claude app tab — it has a ready-made ZIP.
Other agents: place the folder wherever your tool loads Agent Skills from.

Repositoryscienceofapps.com/skills/ai-skills.git · all 200 skills, one folder each, plain git over HTTPS

What it does

The steps it follows

Describe the trend and seasonality in the history.
Pick a simple method (moving average, growth rate, seasonal naive) and say why.
Produce base, high and low forecasts with formulas you can paste into a spreadsheet.
List the assumptions that would change the forecast most.

What you get back

The reply format

What the history shows
Method
Forecast table (base/high/low)
Spreadsheet formulas
Key assumptions

Rules it never breaks

Never present a forecast as certain; always give a range.
Uses only the facts you give it and marks assumptions.

FAQs

Questions about Simple forecast builder

What does the Simple forecast builder skill do?

Teams need a forecast by Friday and either guess or overbuild a model. The skill fixes that: a transparent forecast with method, formulas, base, high and low cases.

How do I install Simple forecast builder in ChatGPT, Claude or Gemini?

Copy the skill and paste it as the first message of a new chat, then send your input. To keep it, paste it into a ChatGPT Project or custom GPT, a Claude Project or a Gemini Gem, or upload the SKILL.md file as a Claude Skill.

What do I send Simple forecast builder after installing it?

Send historical monthly numbers (at least 12 months ideally) and what you need to forecast. If something essential is missing, the skill asks you one short question and then continues.

Is the Simple forecast builder skill free?

Yes. It's free to copy, use and adapt, with no sign-up, and works in the free versions of ChatGPT, Claude, Gemini and Copilot.

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You paste

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You get

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How to use it

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ProblemYou know what you want the spreadsheet to do but not the formula, and nested IFs break.

You paste

Google Sheets: total of column C where column A is 'Mumbai' and column B is in October 2026

You get

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Simple forecast builder

About Simple forecast builder

Copy, paste, send

ChatGPT

Claude

Gemini

Microsoft Copilot

Any other assistant

Install it permanently

Quick setup

Quick setup

Quick setup

Quick setup

The steps it follows

The reply format

Rules it never breaks

Questions about Simple forecast builder

Event tracking plan

SQL from plain English

Spreadsheet formula helper

The Laws of UX, in one field guide

100+ Subscription Paywalls, decoded

About Simple forecast builder

Copy, paste, send

ChatGPT

Claude

Gemini

Microsoft Copilot

Any other assistant

Install it permanently

Quick setup

Quick setup

Quick setup

Quick setup

The steps it follows

The reply format

Rules it never breaks

Questions about Simple forecast builder

Pair it with

Event tracking plan

SQL from plain English

Spreadsheet formula helper

The Laws of UX, in one field guide

100+ Subscription Paywalls, decoded