Merge pull request #4742 from theomart/patch-2

Correct get_min_pair_stake_amount formula

docs/configuration.md

@@ -167,7 +167,7 @@ This exchange has also a limit on USD - where all orders must be > 10$ - which h
 
 To guarantee safe execution, freqtrade will not allow buying with a stake-amount of 10.1$, instead, it'll make sure that there's enough space to place a stoploss below the pair (+ an offset, defined by `amount_reserve_percent`, which defaults to 5%).
 
-With a stoploss of 10% - we'd therefore end up with a value of ~13.8$ (`12 * (1 + 0.05 + 0.1)`).
+With a reserve of 5%, the minimum stake amount would be ~12.6$ (`12 * (1 + 0.05)`). If we take in account a stoploss of 10% on top of that - we'd end up with a value of ~14$ (`12.6 / (1 - 0.1)`).
 
 To limit this calculation in case of large stoploss values, the calculated minimum stake-limit will never be more than 50% above the real limit.
 

freqtrade/exchange/exchange.py

@@ -539,7 +539,9 @@ class Exchange:
         # reserve some percent defined in config (5% default) + stoploss
         amount_reserve_percent = 1.0 + self._config.get('amount_reserve_percent',
                                                         DEFAULT_AMOUNT_RESERVE_PERCENT)
-        amount_reserve_percent += abs(stoploss)
+        amount_reserve_percent = (
+          amount_reserve_percent / (1 - abs(stoploss)) if abs(stoploss) != 1 else 1.5
+        )
         # it should not be more than 50%
         amount_reserve_percent = max(min(amount_reserve_percent, 1.5), 1)
 

tests/exchange/test_exchange.py

@@ -371,7 +371,7 @@ def test_get_min_pair_stake_amount(mocker, default_conf) -> None:
         PropertyMock(return_value=markets)
     )
     result = exchange.get_min_pair_stake_amount('ETH/BTC', 1, stoploss)
-    assert isclose(result, 2 * 1.1)
+    assert isclose(result, 2 * (1+0.05) / (1-abs(stoploss)))
 
     # min amount is set
     markets["ETH/BTC"]["limits"] = {
@@ -383,7 +383,7 @@ def test_get_min_pair_stake_amount(mocker, default_conf) -> None:
         PropertyMock(return_value=markets)
     )
     result = exchange.get_min_pair_stake_amount('ETH/BTC', 2, stoploss)
-    assert isclose(result, 2 * 2 * 1.1)
+    assert isclose(result, 2 * 2 * (1+0.05) / (1-abs(stoploss)))
 
     # min amount and cost are set (cost is minimal)
     markets["ETH/BTC"]["limits"] = {
@@ -395,7 +395,7 @@ def test_get_min_pair_stake_amount(mocker, default_conf) -> None:
         PropertyMock(return_value=markets)
     )
     result = exchange.get_min_pair_stake_amount('ETH/BTC', 2, stoploss)
-    assert isclose(result, max(2, 2 * 2) * 1.1)
+    assert isclose(result, max(2, 2 * 2) * (1+0.05) / (1-abs(stoploss)))
 
     # min amount and cost are set (amount is minial)
     markets["ETH/BTC"]["limits"] = {
@@ -407,10 +407,10 @@ def test_get_min_pair_stake_amount(mocker, default_conf) -> None:
         PropertyMock(return_value=markets)
     )
     result = exchange.get_min_pair_stake_amount('ETH/BTC', 2, stoploss)
-    assert isclose(result, max(8, 2 * 2) * 1.1)
+    assert isclose(result, max(8, 2 * 2) * (1+0.05) / (1-abs(stoploss)))
 
     result = exchange.get_min_pair_stake_amount('ETH/BTC', 2, -0.4)
-    assert isclose(result, max(8, 2 * 2) * 1.45)
+    assert isclose(result, max(8, 2 * 2) * 1.5)
 
     # Really big stoploss
     result = exchange.get_min_pair_stake_amount('ETH/BTC', 2, -1)
@@ -432,7 +432,10 @@ def test_get_min_pair_stake_amount_real_data(mocker, default_conf) -> None:
         PropertyMock(return_value=markets)
     )
     result = exchange.get_min_pair_stake_amount('ETH/BTC', 0.020405, stoploss)
-    assert round(result, 8) == round(max(0.0001, 0.001 * 0.020405) * 1.1, 8)
+    assert round(result, 8) == round(
+        max(0.0001, 0.001 * 0.020405) * (1+0.05) / (1-abs(stoploss)),
+        8
+    )
 
 
 def test_set_sandbox(default_conf, mocker):