diff --git a/library/src/calculator_functions.cpp b/library/src/calculator_functions.cpp
index 5b1a1c7..8d8a712 100644
--- a/library/src/calculator_functions.cpp
+++ b/library/src/calculator_functions.cpp
@@ -231,6 +231,7 @@ std::string Calculator::GetDurationFromCost(Configuration* cfg,
         if (carryOverNotSet) {
             int range = 0;
             int minsToCarryOver = 0; // from one work-time to the other on the same day
+            int minsUsed = 0;
             QDateTime lastCurrent = QDateTime();
 
             auto timeRangeIt = cfg->TimeRange.cbegin();
@@ -246,7 +247,6 @@ std::string Calculator::GetDurationFromCost(Configuration* cfg,
 
                     Q_ASSERT_X(from < to, __func__, "MISCONFIGURED WORK-TIMES");
 
-
                     if (current.time() >= to) {
                         continue; // try to use next available work-time
                     } else
@@ -272,22 +272,23 @@ std::string Calculator::GetDurationFromCost(Configuration* cfg,
                         int duration = timeRange.time_range_to_in_minutes_from_start -
                                        timeRange.time_range_from_in_minutes_from_start;
 
-                        if (current.addSecs(duration * 60).time() <= to) {
-                            for(const auto &x: cfg->PaymentRate) {
-                                ATBPaymentRate const rate = x.second;
-                                if (rate.pra_payment_unit_id == timeRange.time_range_payment_type_id) {
-                                    if (minsToCarryOver > 0) {
-                                        durationMinutes -= minsToCarryOver;
-                                        durationMinutesNetto += minsToCarryOver;
-                                        durationMinutesBrutto += minsToCarryOver;
-                                        current = current.addSecs(minsToCarryOver*60);
-                                        minsToCarryOver = 0;
-                                    } else {
-                                        if (price >= cost) {
-                                            end_datetime = current;
-                                            return end_datetime.toString(Qt::ISODate).toStdString();
-                                        }
+                        if (minsUsed > 0) {
+                            duration -= minsUsed;
+                            minsUsed = 0;
+                        }
 
+                        if (current.addSecs(duration * 60).time() <= to) {
+                            if (minsToCarryOver > 0) {  // the price for this time range
+                                                        // has been is paid already
+                                durationMinutes -= duration;
+                                durationMinutesNetto += duration;
+                                durationMinutesBrutto += duration;
+                                current = current.addSecs(duration*60);
+                                minsToCarryOver = 0;
+                            } else {
+                                for(const auto &x: cfg->PaymentRate) {
+                                    ATBPaymentRate const rate = x.second;
+                                    if (rate.pra_payment_unit_id == timeRange.time_range_payment_type_id) {
                                         price += (uint)rate.pra_price;
 
                                         if (price >= maxParkingPrice) {
@@ -304,8 +305,9 @@ std::string Calculator::GetDurationFromCost(Configuration* cfg,
                                             end_datetime = current;
                                             return end_datetime.toString(Qt::ISODate).toStdString();
                                         }
+
+                                        break;
                                     }
-                                    break;
                                 }
                             }
 
@@ -320,11 +322,13 @@ std::string Calculator::GetDurationFromCost(Configuration* cfg,
 
                             lastCurrent = current;
                             current.setTime(to);
-                            int const minsUsed = lastCurrent.secsTo(current) / 60;
+                            minsUsed = lastCurrent.secsTo(current) / 60;
 
                             // mod duration: possibly discard some minutes in
                             // the next time-range
-                            minsToCarryOver = (durationMinutes - minsUsed) % duration;
+                            if (durationMinutes >= minsUsed) {
+                                minsToCarryOver = durationMinutes - minsUsed;
+                            }
 
                             durationMinutes -= minsUsed;
                             durationMinutesNetto += minsUsed;
@@ -344,12 +348,10 @@ std::string Calculator::GetDurationFromCost(Configuration* cfg,
                                             end_datetime = current;
                                             // return end_datetime.toString(Qt::ISODate).toStdString();
                                         }
-
                                         break;
                                     }
                                 }
                             }
-
                             break;
                         }
                     }