diff --git a/library/src/calculator_functions.cpp b/library/src/calculator_functions.cpp
index 67ac6b3..d9cd1e9 100644
--- a/library/src/calculator_functions.cpp
+++ b/library/src/calculator_functions.cpp
@@ -118,6 +118,15 @@ std::string Calculator::GetDurationFromCost(Configuration* cfg,
                                             bool nextDay,
                                             bool prepaid)
 {
+    // use tariff with structure as for instance Schnau, Koenigsee:
+    // without given YearPeriod, SpecialDays and SpecialDaysWorktime
+    if (cfg->YearPeriod.size() == 0
+        && cfg->SpecialDays.size() == 0
+        && cfg->SpecialDaysWorktime.size() == 0)
+    {
+        return QString().setNum(GetDurationForPrice(cfg, price)).toStdString();
+    }
+
     // Get input date
     QDateTime inputDate = QDateTime::fromString(start_datetime,Qt::ISODate);