How to build a custom GPT for your coaching business. Seven steps, two complete instruction files, and the rule that keeps the file portable.
A coach on r/personaltraining discussing AI programme builders described the useful version of the tool in one line: orchestrate the models into building the programmes and workouts "we develop on our own". A custom GPT is that orchestration saved: your voice, your rules and your files loaded once, so the weekly job opens ready. This page builds one for check-in drafting and one for content, and shows why the instruction file, not the vendor, is the thing to own.
By Markus Evers · Published 6 September 2026 · Updated September 2026
the short version
A custom GPT is a saved ChatGPT with its own instructions, files and starters. A coach builds one in 7 steps when a job repeats weekly: pick the job, write the instruction file, add your own files (never client data), set four starters, test with three prompts, keep it private, review monthly. Start with check-in drafting.
What is a custom GPT, and does a coach need one?
A saved ChatGPT with its own instruction file, knowledge files and conversation starters, opened from the sidebar. A coach needs one when the same job repeats every week with the same rules and the same files; for anything lighter, the two boxes on the ChatGPT custom instructions guide already apply your voice and rules to every chat in five minutes. The test is simple: if you paste the same style card and rule list at the top of a chat twice in one week, build the GPT.
Which job should your first GPT do?
Check-in replies. The first GPT should draft check-in replies, because it is the job with the most repetition, the clearest structure and the highest cost of sounding generic. A client on r/personaltraining who stopped training after their coach began using AI in weekly check-in comments ("it was really the only time we talked") is the failure case; a GPT with your style card, your four-part structure and a rule to stop when pain is mentioned is the working one.
What are the 7 steps to build a coaching custom GPT?
Decide the job, write the file, add your files, set the starters, test, set sharing, review monthly. Steps 2 and 3 carry the work; the two instruction files below are step 2 done.
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1.Decide the one job
One GPT, one job, one output shape. Check-in drafting for most coaches; content drafting second. A GPT that "helps with my coaching business" does nothing well.
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2.Write the instruction file
Start from the two custom-instruction boxes on the custom instructions page, add the job, the input you will paste, the output structure and the rules. The two files below are complete; change the [FIELDS].
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3.Add the knowledge files
Your style card, three of your own samples, your programme templates, your FAQ and offer page. Never a client file, a check-in export or a photo. Name the files exactly as the instruction file expects.
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4.Set four conversation starters
The four requests you will actually make, written as you would type them. They are the buttons you press every week, so they earn their words.
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5.Test with three prompts
One normal check-in, one that mentions pain, one "make it shorter". The three tests below tell you whether the rules hold before a real reply depends on them.
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6.Keep it private, or share with your team
Private for a solo coach. Share by link with a team only if every member follows the same client data rule; a shared GPT is a shared responsibility.
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7.Review monthly
Re-read the instruction file with the last four drafts beside it. Add a rule for every mistake you edited out more than once. Retire the GPT the month it stops saving time.
What goes in the instruction file for a check-in GPT and a content GPT?
Six parts: the name and the one job, who you are, the voice source, the input you will paste, the output structure, and the rules including what makes it stop. Both files below are complete; fill the [FIELDS], upload a style card named as the file expects, and paste the four starters. The style card itself comes from the coaching voice guide.
Instruction file: check-in drafting assistant
When to use it: Paste into the GPT builder instruction field, a Claude Project or a Gemini Gem.
What to paste in: Your niche, method, tone, phrases; upload style-card.txt.
NAME: Check-in drafting assistant JOB: Draft my reply to one client check-in at a time, for me to edit and send. You never send anything and you never decide anything. ABOUT ME I am an online fitness coach. Niche: [YOUR NICHE]. Clients are coached remotely through an app with weekly check-ins. My method in one line: [YOUR METHOD]. Tone: [THREE WORDS]. Phrases I use: [FIVE PHRASES]. Phrases I never use: journey, crush, smash, empower, unlock, game-changer, "you've got this", lists of three, exclamation marks. VOICE Use the style card in the knowledge file "style-card.txt" for length, openers, repeated phrases and sign-off. If the file is missing, ask me for five replies I wrote before drafting anything. INPUT I paste one check-in: the client's first name or initials, the numbers (weight, sessions done of planned, steps, sleep, adherence), their own words, and my one-line read of the week. Nothing else is needed. Do not ask for health history; if the client mentions pain, illness, medication or a condition, stop and tell me to handle it myself. STRUCTURE OF EVERY DRAFT 1. One specific win with its number, in their words where possible. 2. What the numbers show, one or two sentences, no diagnosis. 3. One adjustment for next week and the reason. 4. One ask they can answer with a yes or a number. Length 60 to 140 words. Plain text, no heading, no bullet points, no closing "let me know if you have any questions". RULES Never invent a number, a result or a plan detail I did not give you. Never comment on the client's body. Never give medical or supplement advice. If anything needed for a good reply is missing, ask one question before drafting. Label every output "DRAFT FOR COACH REVIEW" on the first line. If I say "shorter", cut the first sentence first.
Conversation starters for the check-in GPT
When to use it: The four buttons on the GPT's start screen.
What to paste in: Nothing; edit the wording to how you type.
Here is one check-in. Draft the reply. Draft a reply for a week where the client missed most sessions and said they feel like they are failing. Draft a reply for a plateau week with good adherence. Make the last draft shorter and cut the first sentence.
Instruction file: content assistant
When to use it: Paste into the GPT builder instruction field, a Claude Project or a Gemini Gem.
What to paste in: Your niche, offer, pillars, objections, tone, phrases; upload style-card.txt, samples.txt and calendar.txt.
NAME: Content assistant JOB: Draft captions, carousel text, story scripts and newsletter drafts for my coaching account, in my voice, from material I give you. You never post anything. ABOUT ME I am an online fitness coach. Niche: [YOUR NICHE]. What I sell: [YOUR OFFER]. Content pillars: [THREE PILLARS]. My audience's real objections: [THREE]. Tone: [THREE WORDS]. Phrases I use: [FIVE PHRASES]. Phrases I never use: elevate, unlock, journey, game-changer, empower, transform, dive in, seamless, "it's not X, it's Y", "in today's fast-paced world". VOICE Use the knowledge file "style-card.txt" and the three sample captions in "samples.txt" for sentence length, openers and rhythm. Copy the rhythm, never the sentences. INPUT One of: a client question (no name), a mistake I saw this week, a myth and the number behind it, a client win with the consent already given, or a topic from my content calendar in "calendar.txt". Plus the format: caption, carousel (slide count), story script, or newsletter. OUTPUT RULES One draft, not three versions. Under 120 words for a caption, under 40 words per carousel slide, under 200 words for a newsletter. Start with the specific detail, never with a question. No hashtags in the body; five on a separate last line if I ask. No emoji unless my samples have them. No summary sentence, no "drop a comment", no promise of results, no invented client, number or study. Health claims only as I stated them. Label the output "DRAFT FOR COACH REVIEW". WHEN UNSURE If the material is thin, say what is missing in one line and stop. Do not fill gaps with generic fitness advice.
Conversation starters for the content GPT
When to use it: The four buttons on the GPT's start screen.
What to paste in: Nothing; edit the wording to how you type.
Turn this client question into a caption. Turn this mistake I saw three times this week into a 6-slide carousel. Write this week's 200-word newsletter from these notes. Give me one story script from this myth and the number behind it.
What files should you upload, and what never?
Upload your own material: the style card, three samples of your writing, your programme templates, your FAQ, your offer page, your content calendar. Never upload a client file, a check-in export, a progress photo, a payment record or a message thread, and never paste one into a chat with the GPT either; the client data guide has the 14-row yes and no table and the anonymisation template. Both instruction files tell the GPT to stop when a client mentions pain, illness, medication or a condition, which is the second line of defence; the first is what you never paste. The account settings behind the GPT, including why project-only memory is not a privacy boundary, are in the memory and privacy settings guide.
Should clients use your GPT?
Not for anything about their health, training or nutrition. A client-facing GPT that answers those questions is advice you never saw, under your name. Tell clients about your AI use in one paragraph instead, using the AI use policy template, and keep every GPT coach-side.
The three tests before a real reply depends on it
- 1.Paste a real check-in with the name replaced by initials and no health details. A good GPT returns one labelled draft in your structure and voice; a bad one adds numbers you did not give it.
- 2.Paste a check-in that mentions knee pain. A good GPT stops and tells you to handle it yourself; a bad one drafts advice.
- 3.Type "make it shorter" after a draft. A good GPT cuts the first sentence first and keeps the ask; a bad one rewrites everything.
Custom GPT, Claude Project or Gemini Gem: which home?
The one your plan already pays for, because the instruction file is the same text in all three. Write it once as plain text, keep it in a note, and paste it wherever you work this year. A 520-upvote r/ChatGPTPro thread titled "I'm done. Switching to Claude" ran 262 comments on limits and models, and its top reply warned that Claude Pro session limits "are quite low when compared to ChatGPT Plus"; another said managing tokens "is a nightmare". Limits and models change; a portable file does not. The ChatGPT versus Claude comparison covers the coaching-specific differences. The Gemini home, with the four gems and the Google tools each reads, is written out in Gemini Gems for fitness coaches.
| Home | Where the file goes | Your files | Starters | Notes |
|---|---|---|---|---|
| ChatGPT custom GPT | Instruction field in the GPT builder | Knowledge files | Yes, four | Shareable by link; check the current plan page for who can build |
| Claude Project | Project instructions (system prompt) | Project knowledge | No; keep them in a note | Coaches on r/ChatGPTPro report tighter session limits on the Pro plan; plan the week around it |
| Gemini Gem | Gem instructions | Attached files | No; keep them in a note | Same file, same structure; test the pain-mention rule, since models differ in how strictly they follow a stop instruction |
Plan limits, prices and which plans can build or share GPTs change often; check each vendor's current plan page rather than this table for those.
Where do the outputs go?
Into the client thread, after you have read and edited them, and nowhere else. The GPT drafts; the coaching record stays in the platform. On Coachway the check-in the GPT drafted a reply for, the reply itself and the client's next week sit in one client record, so the draft's numbers come from the check-in form and the edited reply goes back into the same thread. The check-in reply prompts are the manual version of the same job for the weeks you are away from the GPT.
Frequently asked questions about custom GPTs for coaches.
What is a custom GPT?
A saved version of ChatGPT with its own instructions, knowledge files and conversation starters, built in the GPT builder and opened from your sidebar. It does not learn on its own; it does exactly what the instruction file says every time. For a coach it is the difference between re-explaining your voice and rules in every chat and opening one that already knows them.
Is a custom GPT free?
Building and sharing custom GPTs has been a paid-plan feature; using GPTs that others share has been open more widely. Both have changed more than once, so check the current plan page before deciding. The instruction files on this page also work as a Claude Project or a Gemini Gem, so the plan you already pay for is usually the right home.
Can clients use my custom GPT?
Not for anything about their health, training or nutrition. A client-facing GPT that answers those questions is you giving advice you never saw, under your name. Keep GPTs coach-side, tell clients about your AI use in one paragraph, and give them a human for every question that matters. A shared FAQ GPT about your booking hours and policies is the most a client should ever get.
Can a custom GPT see my client data?
Only what you paste or upload, and you should paste and upload none of it. Knowledge files are for your own material: programme templates, your FAQ, your offer page, your style card. Client names, photos, health details and payment details never go in a file or a chat; the client data guide on this site has the yes and no table. The instruction files here tell the GPT to stop if a client mentions a condition.
Custom GPT or custom instructions: which first?
Custom instructions first, because they take five minutes and cover most coaches: two boxes that apply to every chat. Build a GPT when one job repeats every week and needs its own files and starters, which for most coaches is check-in drafting. If you find yourself pasting the same style card and rules at the top of a chat twice a week, that is the signal to build.
Can I move my GPT to Claude or Gemini?
Yes, if you wrote it as a plain instruction file. The same text goes into a Claude Project as the system prompt with the same files attached, or into a Gemini Gem as its instructions. Conversation starters do not transfer, but they are four lines. Coaches on r/ChatGPTPro who switched models reported that limits, not features, drove the move, which is why the file, not the vendor, is the thing to own.
Do custom GPTs remember conversations?
A GPT does not carry memory between chats on its own; it starts each chat from its instruction file and knowledge files, which is what you want for client work. ChatGPT's separate memory feature can still note things across your account depending on your settings, so turn memory off for client-adjacent work or use a temporary chat, and delete any saved memory that mentions a client.
One job, one file, your files only. Own the instruction file and every model is a place to run it.
Keep reading
all guidesChatGPT Custom Instructions for Fitness Coaches (2026 Setup)
The complete copy-paste ChatGPT setup for an online fitness coach: the "about you" and "how to respond" boxes at about 1,400 characters each, four Project instruction blocks (content, client comms, programming assistant, business admin), what to upload and never upload, the same setup in Claude and Gemini, memory and privacy hygiene, and a five-minute test.
Read the guideChatGPT Prompts for Client Check-In Replies: 10 Prompts + Tone Training
Ten ChatGPT prompts that turn a stripped check-in form into a reply in your voice, each locked to the acknowledge, assess, one adjustment, one ask structure, plus a tone-training prompt that builds a style card from five of your own replies, the paste-in and keep-out rules, and a slipping-client prompt that gives bullet points instead of a message.
Read the guidePrompt engineering for fitness coaches: the 6-part coach prompt
The six parts every coaching prompt needs as a fill-in template, three bad-versus-good pairs, the ten mistakes coaches make, the argue-back add-on, and the map of which prompt page to use for which job.
Read the guideFree tools for this: Personal Trainer Income Calculator · Client Capacity Calculator · Client Churn Rate Calculator
Ready-made template: AI Use Policy Template for Coaches
Where the check-in comes from
Check-in forms, the numbers and the client thread in one record, so the draft has its inputs and the edited reply has its home. Start the 14-day free trial; cancel any time under Billing.
