# How is the amount of interest determined when withdrawing?

**URL:** <https://governance.aave.com/t/how-is-the-amount-of-interest-determined-when-withdrawing/11221>\
**Category:** Learning Center\
**Created:** [December 31, 2022, 5:47pm UTC](https://governance.aave.com/t/how-is-the-amount-of-interest-determined-when-withdrawing/11221 "2022-12-31T17:47:05Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![curubas](https://avatars.discourse-cdn.com/v4/letter/c/f4b2a3/32.png) [@curubas](https://governance.aave.com/u/curubas)\
**Post date:** [December 31, 2022, 5:47pm UTC](https://governance.aave.com/t/how-is-the-amount-of-interest-determined-when-withdrawing/11221/1 "2022-12-31T17:47:05Z")

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Suppose that you supply 10 USDT in the day 1

This implies create a tx where you send **10 USDT** and receive **10 aPolUSDT**

On day 365 in the dashboard you can see that now you have 11 USDT (10% APY) and want withdraw all.

Then a transactions that call withdrawal method is created, you send **10 aPolUSDT** and receive **11 USDT** , how this 1USDT of interest is calculated?

For a more real example see this tx [0x5bcb11579fa60fa55ba83bdc0140aa9bafaa493d85cdb899a65a463551206871](https://polygonscan.com/tx/0x5bcb11579fa60fa55ba83bdc0140aa9bafaa493d85cdb899a65a463551206871), send 3.202497 aPolUSDT and receive 3.20501 USDT how the 0.00251 of interest is calculated?

Thanks!

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<div class="post-metadata">

**Author:** ![sakulstra](https://dub1.discourse-cdn.com/flex013/user_avatar/governance.aave.com/sakulstra/32/2002_2.png) [@sakulstra](https://governance.aave.com/u/sakulstra)\
**Post date:** [January 1, 2023, 12:26am UTC](https://governance.aave.com/t/how-is-the-amount-of-interest-determined-when-withdrawing/11221/2 "2023-01-01T00:26:50Z")

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In theory it’s this formula [APY and APR - Developers](https://docs.aave.com/developers/v/2.0/guides/apy-and-apr#apr-greater-than-apy)

That said in practice it’s unusable as utilization and thus rate is highly dynamic so calculation via growth index [SDKs - Developers](https://docs.aave.com/developers/v/2.0/getting-started/sdks#rates-calculation) is more realistic scenario. Especially as otherwise flash and portal fees would be ignored.  
The pool essentially tracks the index on the accounts last action per asset so together with current index you can get the archived rate.