> ## Documentation Index
> Fetch the complete documentation index at: https://docs.thunderphone.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Add funds and turn on auto top-up

> Pay-as-you-go billing: add a card, load your balance, and set auto top-up so a call never dies mid-sentence.

ThunderPhone billing is pay-as-you-go: calls draw from your
organization's balance at your agent's per-minute rate. No
subscriptions, no seats. Everything on this page lives under
**Organization → Billing Settings**.

## 1. Add a card

A card unlocks top-ups and phone numbers. It's only charged when you
add funds — **never automatically** (unless you later opt into auto
top-up).

## 2. Load your balance

Click one of the preset amounts ($25–$1000) or enter your own, then
**Add to balance** — a confirmation dialog shows exactly what you're
about to charge before you click **Confirm and charge**. Add at least
**\$3.00** to start making real calls. Funds never expire.

<Note>
  What a minute costs depends on the agent: engine tier plus
  surcharges (for example,
  [premium languages](/guides/supported-languages) add 2¢/min). The
  agent builder shows each agent's all-in rate live. Running
  [outbound campaigns](/guides/outbound-campaigns)? Every campaign
  call draws from this same balance, so size your top-ups (or auto
  top-up) to the list you're dialing. Widget `context` is truncated at
  12,000 characters and counts toward prompt-size pricing.
</Note>

## 3. Turn on auto top-up (optional, recommended)

If the balance hits zero mid-call, the call dies. Auto top-up prevents
that:

<Steps>
  <Step title="Enable the switch">
    Flip **Enable auto top-up**.
  </Step>

  <Step title="Set the trigger and refill">
    Choose **When balance falls below** (the threshold) and **Add
    amount** (the refill). When the balance dips under the threshold,
    ThunderPhone charges your card for the refill amount.
  </Step>

  <Step title="Optionally cap the month">
    Check **Monthly spending limit** to bound how much auto top-up can
    spend per calendar month.
  </Step>

  <Step title="Save">
    Click **Save changes**.
  </Step>
</Steps>

## Prompt-size surcharge

Per-minute call rates cover agent prompts up to 5,000 tokens. Larger
prompts add a per-minute surcharge: each additional block of 10,000
tokens (or part of one) adds **+1¢/min** on Spark and **+2¢/min** on
Bolt and Storm.

The surcharge is computed from the prompt actually used on each call.
That includes page `context` supplied by an embedded
[web widget](/guides/embed-web-widget), which is capped at 12,000
characters (roughly 3,400 tokens of typical English text). The prompt
editor in the dashboard shows a live estimate while you edit, and each
call's billing-history entry breaks out widget-context tokens.

## Watch the money

The **Billing History** tab lists every transaction — top-ups
(manual and automatic), per-call usage, and monthly phone-number
charges. The same data is available programmatically via the
[Billing API](/api-reference/billing).

***

## Next steps

<CardGroup cols={2}>
  <Card title="Get a phone number" icon="phone" href="/guides/get-a-phone-number">
    With funds loaded, numbers are a click away.
  </Card>

  <Card title="Billing API reference" icon="code" href="/api-reference/billing">
    Balance, top-ups, auto-reload, and transactions over REST.
  </Card>
</CardGroup>