> ## Documentation Index
> Fetch the complete documentation index at: https://second.tech/docs/llms.txt
> Use this file to discover all available pages before exploring further.
# Fees and limits
> Read the fee lines in a Swaptopia quote, see what Second's Ark server charges for a swap, and check the amount limits before you start one.
Swaptopia adds no fee of its own. Every fee line in the quote is charged by the Ark server or paid to miners.
## Read the quote
When you enter an amount under **You send**, the quote fills in **You receive** with every fee line. To receive a set figure instead, enter it under **You receive**. Swaptopia then works out the smallest **You send** amount that pays it out, with the fees on top. Each direction has its own fee lines. Select the **Swap direction** button to read the other set.
* **Boarding transaction (miner fee):** An estimate of the miner fee of the transaction that [boards](/docs/learn/board) your bitcoin onto Ark. The feerate can change before Swaptopia boards your bitcoin.
* **Service fee 0.5%:** The Ark server's fee for paying your Lightning invoice, as listed on [Second's pricing page](https://second.tech/pricing).
* **Service fee 0.5%:** The Ark server's fee for the on-chain payout to your address, as listed on [Second's pricing page](https://second.tech/pricing).
* **On-chain miner fee:** An estimate of the miner fee of the payout transaction to your address. The feerate can change before the payout goes out.
The **Fee paid** line on the receipt replaces the estimate with the fees Swaptopia recorded during the swap. For a bitcoin-to-Lightning swap, that is the Lightning service fee, plus the boarding miner fee when Swaptopia could measure it. For a Lightning-to-bitcoin swap, it is the service fee and miner fee of the on-chain payout.
## Service fee
The quote shows a 0.5% service fee, the rate Second's Ark server charges on bitcoin with 14 days or more of its [lifetime](/docs/learn/lifetime) left. Bitcoin with less lifetime left pays a lower rate, which the **Fee paid** line on the receipt reflects.
The same goes for [leftover sats](/docs/swaptopia/wallet#send-leftover-sats) you send on their own, whose fee can come out lower than the percentage in the label. The full schedule is on [Second's pricing page](https://second.tech/pricing). [Ark fees](/docs/learn/fees) explains why the rate depends on lifetime.
On small Lightning payouts, the Ark server charges a 20-sat minimum fee instead of the percentage. The line then reads **Service fee (minimum 20 sats)**.
## Miner fees
Each direction's quote carries one miner fee:
* **Boarding transaction (miner fee):** Swaptopia prices the board at the current 3-block feerate from Second's Esplora server (mempool.second.tech on mainnet), or higher if its wallet estimates more. This fee comes out of the bitcoin that arrives. Your on-chain wallet app pays its own miner fee on top to reach the funding address.
* **On-chain miner fee:** The Ark server charges the miner fee of the payout transaction to your address as part of the swap.
If the quote says the boarding transaction's miner fee "cannot be priced right now", **Swap** stays disabled. Wait a moment, then edit the amount or select a preset to quote again.
## Amount limits
Swaptopia checks your amount against these limits and tells you which one you hit.
The Ark server accepts a board of at least 50,000 sats on mainnet (10,000 on signet), counted after the boarding transaction's miner fee comes out. So a bitcoin-to-Lightning swap adds room for that fee: at least 1,000 sats, and more once the feerate passes about 2 sat/vB. If you enter less, Swaptopia raises the amount to the smallest one that boards. A note on the swap card says so.
| Limit | Mainnet | Signet |
| - | - | - |
| Minimum bitcoin-to-Lightning swap | At least 51,000 sats, more when the feerate is above about 2 sat/vB | At least 11,000 sats, more when the feerate is above about 2 sat/vB |
| Maximum per swap | 10,000,000 sats (0.1 BTC) | 100,000,000 sats (1 BTC) |
| Maximum Lightning payment received (Lightning to bitcoin) | 2,750,000 sats | Set by the signet Ark server |
| On-chain payout minimum | 1,000 sats after fees | 1,000 sats after fees |
| Lightning payout minimum | 1 sat after the 20-sat minimum Lightning fee | 1 sat after the 20-sat minimum Lightning fee |
| Minimum amount under **You send** | 100 sats | 100 sats |
## Preview mainnet fees from signet
On signet, Swaptopia can quote a swap at mainnet rates while your test bitcoin stays on signet, so you see the real cost before you switch.
The link sits under the **Swap** button. A banner confirms the preview. The status bar reads **mainnet preview**.
The quote shows mainnet fee lines, as described in [Read the quote](/docs/swaptopia/fees-and-limits#read-the-quote). **Swap** stays disabled during the preview.
Swaptopia closes the banner and quotes from the signet server again.
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