Moving on to Slide 12, we provide an update on the rate commentary. Rating trends in Q3 have remained broadly similar to the first half of 2023. Average rate increases were around 7% for our portfolio, excluding the North America programs business. North America program business saw 6% rate increases during Q3, excluding cyber and workers’ compensation, which have both been under pressure, and we are taking portfolio actions to manage the profitability of our book. U.S. property cat rates have remained strong at 20%, while non-U.S. property cat rates have been up 6% during the quarter. Next, Slide 13 shows the change in combined ratio versus ‘22 nine months ended for our core business and breaks the movements into individual subcomponents.
Our portfolio actions are yielding positive results as the combined ratio for our core business on a like-for-like basis has improved by 12 points year-over-year. Our headline combined ratio of 87.6% has benefited from 6 percentage points of reserve releases linked to the LPT transaction. However, the expense reallocation of $29 million results in around 2 percentage points drag. Adjusting for these two results, on a like-for-like combined ratio of 91.9%, which compares to 103.9% for the nine months of 2022. Attritional loss ratio was higher at 63.4% or 0.9 points up on the previous year, and is partly impacted from mix changes between insurance and services and the Reinsurance segment and also from large losses in the international business.
The mix changes resulted in better profit commissions which are captured in the acquisition cost ratio, which has resulted in around 1.5 points improvement. Looking at both of the moving parts together, results in a net improvement of 0.5 point year-on-year. We look at the investment portfolio and investment results on slides 13 and 14. We have made progress as we delivered a strong net investment income figure, increased our overall asset duration to 2.7 years from 2.5 years at Q2 2023 and locked in attractive reinvestment yields in excess of 4.5% on our investment. Total investment result is higher at $208 million versus a loss of $375 million in the prior year’s same period and supported by higher net investment income. We have continued to rotate our portfolio and have now invested over $1.5 billion year-to-date and increased our exposure to corporates and asset-backed securities.
Overall, our investment strategy remains unchanged and focused on maintaining a high-quality fixed income portfolio. 74% of our investment portfolio is now fixed income, of which 97% is investment grade with an average credit rating unchanged at AA. P&L volatility is significantly lower versus last year and has helped given 88% [ph] of the fixed income portfolio is now designated as available from 85% at Q2 ‘23 and none at year-end 2021. Moving on to Slide 15, which looks at our balance sheet, our balance sheet is strong, ending the quarter with $2.3 billion of shareholders’ equity, which is stable since the prior quarter. Total capital including debt was $3 billion. Our issued debt is unchanged, while our debt-to-capital ratio is stable at 25.3% and remains within our target range.
With this, we conclude the financial section of our presentation. Our results continue to be strong. We are on track to deliver significant improvement in profitability in 2023 with only one quarter to go. We are close to our goal to achieve double-digit return on average common equity for the full year, including the benefit of the loss portfolio transfer. As we plan for next year, we expect to realize full run rate benefits of all our strategic actions in 2024 as well as deliver a double-digit return on average common equity. I would like to thank you again for your time this morning. For any questions, please contact our Investor Relations team at investor.relations@siriuspt.com. I will now turn the call back over to the operator.
Operator: Thank you, sir. Ladies and gentlemen, that then concludes today’s conference. Thank you for joining us. You may now disconnect your lines.
