To estimate your monthly AI chatbot bill, take the number of conversations in your busiest month, multiply by the share the AI will handle to the end or by the replies per conversation, depending on how the vendor counts, and then add seats and add-ons. The three common pricing units, per resolution, per credit and flat allowance, each need a slightly different sum. Below is the formula for each, then one worked example run through all of them.
Our post on how AI chatbot pricing models work explains why the models behave differently. This one is the arithmetic.
The three numbers you need first
Every estimate starts from the same inputs. Gather them from your own records, not a vendor's calculator.
- Conversations per month (C). Count chats, contact form messages and support emails that a chatbot could plausibly have handled. Use the busiest month of the last year, not the average.
- Replies per conversation (R). Read 20 real threads and count the back-and-forth. If you have no history, start with 3 and correct it after a month.
- AI share (A). The fraction of conversations the AI handles to the end without a person. If you don't know, use 1 (all of them). That gives a ceiling.
Write these down. Every vendor's pricing page can then be turned into a monthly number in two minutes.
The formula for each pricing model
| Pricing model | Monthly cost formula | What drives it |
|---|---|---|
| Per resolution or outcome | C x A x price per resolution, plus seats | Conversations the AI finishes |
| Message credits | C x R x credits per reply, then the plan that covers it, plus top-ups | Replies, and which AI model you pick |
| Per conversation or session | C x price per conversation | Every conversation, resolved or not |
| Flat allowance | Fixed fee, as long as C x R fits the allowance | Only whether you fit the tier |
Two notes. Per-resolution models usually don't charge for conversations that end with a person, so a lower AI share lowers the bill. And credit models often charge more credits per reply for stronger AI models, so the model choice is a pricing decision.
A worked example at 400 conversations
Assume a hypothetical shop with C = 400 conversations in its busiest month, R = 3 replies each, and A = 0.7, meaning the AI finishes 280 of them. Prices below are from each vendor's own pricing page at the time of writing (October 2026). Check those pages before you budget, because they change.
Per resolution.
- Intercom's pricing page lists Fin at $0.99 per outcome: 280 x $0.99 = $277.20, plus Intercom seats.
- Zendesk's pricing page lists automated resolutions at $1.50 committed or $2.00 pay-as-you-go, with a small number included per agent: roughly 280 x $1.50 = $420 or 280 x $2.00 = $560, plus agent seats.
- Help Scout's pricing page lists AI resolutions at $0.75: 280 x $0.75 = $210, plus its per-user plan fees.
Message credits. Every reply the AI sends uses credits, including in conversations that later go to a person. That is C x R = 1,200 replies. Chatbase's pricing page lists its entry tier at $40 a month for 700 credits, with extra credits at $40 per 1,000. On a model that costs 1 credit per reply, 1,200 credits means the entry tier plus one top-up: $80 a month. On a 2-credit model it is 2,400 credits, so $40 plus two top-ups, $120, or a move to the next tier.
Flat allowance. SpideyChat meters AI tokens and averages about 1,335 tokens per reply in production. 1,200 replies is roughly 1.6M tokens. That is more than Starter's 1M (about 750 replies) and comfortably inside Pro's 5M (about 3,750 replies), so the bill is $29.99 a month.
| Model | Example vendor | Monthly estimate before seats and add-ons |
|---|---|---|
| Per outcome | Intercom Fin | $277.20 |
| Per resolution | Zendesk (committed) | about $420 |
| Per resolution | Help Scout | $210 |
| Credits, 1 per reply | Chatbase | $80 |
| Flat | SpideyChat Pro | $29.99 |
These products are not identical. Intercom, Zendesk and Help Scout are full helpdesks with inboxes and seats, and that is part of what you pay for. SpideyChat is a website chatbot that answers from your content, captures leads, opens numbered tickets and hands over to a person when one is online. Compare like with like on features before comparing totals.
Add what the formula leaves out
The per-reply or per-resolution number is rarely the whole bill. Add these line by line:
- Seats. Helpdesk tools charge per agent. Two people on a mid tier can cost more than the AI itself.
- Branding removal. Some vendors charge a monthly add-on to remove their name from the widget. Chatbase's pricing page lists it at $99 a month.
- Extra bots or websites. Check how many chatbots and sites the tier allows.
- Top-ups versus a hard stop. Find out whether going over the allowance bills you more or pauses the bot. Flat plans like SpideyChat's pause replies until next month or an upgrade, which caps the cost but means watching usage.
Stress-test the estimate
Run the sums again with two changes. Double C, to see what a good month or a viral post does. Then set A to 1, as if the AI resolved everything. Per-resolution and credit bills rise in a straight line with both changes. A flat bill stays put until you cross a tier, which is the trade-off covered in what per-conversation pricing does in busy months. For a detailed run of the per-outcome case, see Intercom Fin pricing explained.
To put the cost against what a chatbot saves you, the free chatbot ROI calculator takes your volumes and hourly costs.
When you have your three numbers, compare them with the allowances on the SpideyChat pricing page, which lists each plan's tokens and approximate replies so you can see which tier your volume fits.