每日复利循环

我正在做一个项目，我必须计算交易的年至今每日复利。目前我只得到没有利息的当前余额。我相信我的问题是与foreach循环，但我不确定我犯了一个错误。它是通过天，但要么没有兴趣申请或runningTotal没有正确结转。

                public IEnumerable<DateTime> EachDay(DateTime from, DateTime thru)
    {
        for (var day = from.Date; day.Date <= thru.Date; day = day.AddDays(1))
            yield return day;
    }
    public decimal PrincipalplusInterest()
    {
        DateTime startDate = new DateTime( DateTime.Now.Year, 1, 1);
        DateTime endDate = startDate.AddYears(1);
        int compoundingTimes = 12;
        TimeSpan duration = endDate - startDate;
        var numberOfDaysInYear = duration.Days;
        decimal runningTotal = 0;
        double interestRate = InterestRate;
        foreach (DateTime day in EachDay(startDate, endDate))
        {
            decimal sumOfAnyTransactionToday = Transactions.Where(x => x.TransactionDate == day).Sum(x => x.Amount);
            runningTotal = runningTotal + sumOfAnyTransactionToday;
            double timePeriod = 1 / numberOfDaysInYear;
            double rate = interestRate / compoundingTimes;
            double total = System.Convert.ToDouble(runningTotal);
            double principalAndInterest = total * Math.Pow((1 + rate), (compoundingTimes * timePeriod));
            runningTotal = System.Convert.ToDecimal(principalAndInterest);
        }
        return runningTotal;
    }

    [DisplayName("Year to Date Interest")]
    public decimal YrToDateInterest()
    {
        decimal interest = PrincipalplusInterest() - CurrentBalanceCalculation();
        return interest;
    }