later in this footnote. The factors considered include the age of the loan, interest rate, loan size, payment structure, term, risk ratings, loan to value, collateral type, geographical pattern and industrial sector. The breakdown of the loan classes into portfolio segments was a judgement election based upon identified risk criteria. The Company has limited specific historical loss experience to directly tie to an attribute and thus the use of one factor over another is based on management’s perceived risk of the identified factor in combination with the data analyzed.
After consideration of the factors previously discussed, the Company segmented the portfolio based on the identified risk characteristics present within each segment. These risk characteristics are determined based on various factors including call code, collateral types and loan terms. The Company believes that this segmentation best represents the portfolio segments at a level to develop the systematic methodology in the determination of the ACL.
Historical net losses are used to calculate a historical loss rate for each vintage within each portfolio segment and then subjective adjustments for internal and external qualitative risk factors are applied to the historical loss rates to generate a total expected loss rate for each vintage within each portfolio segment. For portfolio segments of loans with no historical losses, the Company is using the weighted average of its annual historical loss rates as a proxy loss rate floor, or specifically, for oil and gas and oil and gas real estate portfolio segments, historical average loss rate based on peer group data.
There are multiple qualitative factors, both internal and external, that could impact the potential collectability of the underlying loans. The various internal factors that may be considered include, among other things: (i) effectiveness of loan policies, procedures and internal controls; (ii) portfolio growth and changes in loan concentrations; (iii) changes in loan quality; (iv) experience, ability and effectiveness of lending management and staff; (v) legal and regulatory compliance requirements associated with underwriting, originating and servicing a loan and the impact of exceptions; and (vi) the effectiveness of the internal loan review function. The various external factors that may be considered include, among other things: (i) current national and local economic conditions; (ii) changes in the political, legal and regulatory landscape; (iii) industry trends, in particular those related to loan quality; and (iv) forecasted changes in the economy.
As part of its assessment, the Company considers the need to adjust historical information to reflect the extent to which current conditions and forecasts differ from the conditions that existed for the period over which historical information was evaluated. The Company uses an economic forecast qualitative factor as noted above to adjust the expected loss rates for the effects of forecasted changes in the economy. The Company uses economic indicators and indexes including, but not limited to, inflation indexes, unemployment rates, fluctuations of interest rates, economic growth, government expenditures, gross domestic product indexes, productivity indicators, leading indexes and debt levels and narratives such as those supplied by the Federal Reserve’s beige book and Moody’s Analytics that provide information for determining an appropriate impact ratio for macro-economic conditions. The Company determined that a two-year forecast period provides a balance between the level of forecast periods reasonably available and forecast accuracy and choose to revert to historical levels immediately afterward as adjusted current loss history is the more relevant indicator of expected losses beyond the forecast period.
The historical loss rates, adjusted for current conditions and forecasting assumptions, are multiplied by the respective loan’s amortized cost balances in each vintage within each segment to compute an estimated quantitative reserve for expected losses in the portfolio. The quantitative reserve for expected credit losses and the qualitative reserve for expected credit losses combined together make up the total estimated credit loss reserve.
Loan amortized costs, as defined by GAAP, includes principal, deferred fees or costs associated with the loan, premiums, discounts and accrued interest. The Company made a policy election to exclude accrued interest and deferred fees and costs in the determination of an ACL. The Company continues its policy of reversing previously accrued interest when it has been deemed uncollectible. Loans held for sale are excluded from the computation of expected loan loss as they are carried at the lower of cost or market value.
As part of the implementation of CECL, the Company changed its methodology for determining the ACL for loans. As a result of the adoption of CECL, the ratio of the ACL for loans to total loans increased from 0.96% at December 31, 2019 to 0.99% at January 1, 2020. At September 30, 2020, the ratio of the ACL for loans to total loans was 1.49%, reflecting the expected impact of COVID-19 and the sustained instability in the oil and gas industry during 2020 on the local and national economy and on current and forecasted expected credit losses. Additionally, the increase in adversely graded loans within the portfolio has resulted in an increase in the ACL related to those individually evaluated loans. The