# Buy SMS units (/guides/sms/buying-units)

SMS is prepaid. Your organisation's **wallet** holds **units** — one unit sends one SMS part (up to 160 characters) to one number. There are no monthly fees.

## Check your balance [#check-your-balance]

Go to **SMS → Wallet**. **Available Balance** shows the units you have left. Below it you'll see everything credited and spent in **Transaction History**.

![SMS Wallet with balance and transaction history](</_next/static/media/sms-04.01dtydmbc8--k.png>)

## Buy units [#buy-units]

1. In **SMS → Wallet**, find **Buy SMS Units**.
2. Enter a **Quantity**. The price per unit and the total update as you type — the more you buy, the lower the price per unit (see the **Pricing Tiers** table).
3. Click **Buy & Pay Now** to pay straight away, or **Add to Cart** to pay later with an invoice.

![Buy SMS Units with the pricing tiers](</_next/static/media/sms-05.0unzodl94ywdd.png>)

Prices shown are **before VAT**. VAT is added on the invoice.

### Pay now [#pay-now]

A secure payment window opens. Pay by **M-Pesa**, card or bank transfer. When payment is confirmed you'll see *"Payment confirmed! SMS units credited."* and your balance updates.

### Pay by invoice [#pay-by-invoice]

1. Click **Add to Cart**, open the cart, and click **Checkout & Create Invoice**.
2. Find the invoice in **Management → My Invoices** and click **Pay**.
3. Choose **Card / Mobile Money** (M-Pesa) or **Bank Transfer** (our bank details are shown).

Units are credited once the payment is confirmed.

## Low-balance alerts [#low-balance-alerts]

So you never run out mid-campaign, turn on alerts in **SMS → Wallet → Low-Balance Alerts**:

1. Tick **Enable low-balance alerts**.
2. Set the **Threshold (Units)** — e.g. 500.
3. Optionally tick **Also send SMS alert**.
4. Click **Save Settings**.

We'll email your organisation's billing contact and admins when the balance drops below the threshold. (Only organisation admins see this setting.)

## How many units will I use? [#how-many-units-will-i-use]

| Message length | Units per recipient |
|---|---|
| Up to 160 characters | 1 |
| 161 – 306 characters | 2 |
| 307 – 459 characters | 3 |

Units are used when a message is sent to the network — even if the phone is off and it later fails. Numbers that have [opted out](./opt-outs.mdx) are skipped and never charged. Quick Send shows the exact cost before you send.