diff --git a/library/src/calculator_functions.cpp b/library/src/calculator_functions.cpp
index 03213af..4c8df6a 100644
--- a/library/src/calculator_functions.cpp
+++ b/library/src/calculator_functions.cpp
@@ -453,10 +453,47 @@ Calculator::ComputeDurationFromCost(Configuration *cfg,
     netto_parking_time_in_minutes = 0;
     brutto_parking_time_in_minutes = 0;
     free_parking_time_in_minutes = 0;
+    int nettoParktimeForCost = 0;
 
-    int const nettoParktimeForCost = priceNettoParktime[int(cost)];
-    qCritical() << __func__ << ":" << __LINE__ << QString("cost=%1 nettoParkTimeForCost=%2").
-                                                        arg(cost).arg(nettoParktimeForCost);
+    if (priceNettoParktime.contains(int(cost))) {
+        nettoParktimeForCost = priceNettoParktime[int(cost)];
+        qCritical() << __func__ << ":" << __LINE__ << QString("cost=%1 nettoParkTimeForCost=%2").
+                                                            arg(cost).arg(nettoParktimeForCost);
+    } else {
+
+        // cannot find netto-parking time for cost (=price)
+        // this happens for direct coin input and should not happen otherwise
+        // take the value for the nearest value of cost and mark result as overpaid
+
+        QList <int> keys = priceNettoParktime.keys();   // keys (=prices) are sorted in ascending order
+        QSet<int> s; // make keys unique
+        for (int k = 0; k < keys.size(); ++k) {
+            if (keys[k] < cost) {
+                s << keys[k];
+            }
+        }
+        keys = s.values();
+        // sort in descending order
+        std::sort(std::begin(keys), std::end(keys), std::greater<>());
+        // qCritical() << __func__ << ":" << __LINE__ << "keys=" << keys;
+        if (!keys.isEmpty()) {
+            int const maxCost = keys[0];
+            auto const p = priceNettoParktime.equal_range(maxCost);
+            for (auto it = p.first; it != p.second; ++it) {
+                nettoParktimeForCost = std::max(nettoParktimeForCost, it.value());
+            }
+            ATBPaymentOption &po = cfg->getPaymentOptions(paymentOptionIndex);
+            po.pop_max_price = maxCost;
+            cfg->getPaymentOptions(paymentOptionIndex).pop_max_price = maxCost;
+            if (pop_allow_overpay) {
+                overPaid = true;
+            }
+            qCritical() << __func__ << ":" << __LINE__ << QString("cost=%1 -> maxCost=%2 nettoParkTimeForCost=%3").
+                                                            arg(cost).arg(maxCost).arg(nettoParktimeForCost);
+        } else {
+            qCritical() << __func__ << ":" << __LINE__ << "ERROR empty keys -> check tariff file";
+        }
+    }
 
     int cnt = 0;
     while (++cnt < 20 && netto_parking_time_in_minutes < nettoParktimeForCost) {