Thanks, Doug. Good morning. Welcome to Progressive’s first quarter conference call. We appreciate you joining us.
During our fourth quarter call, we took the opportunity to reflect on 2020 and the emotional toll of the pandemic and social unrest.
Now with the first quarter of 2021 behind us, we look forward with the optimism that the vaccine rollout brings and the hope of a return to normalcy.
Our people are showing tremendous resilience in the face of hardships and a willingness to react to whatever comes next for the positive attitude, which allow us to continue to deliver fantastic results.
This quarter, our net premiums written growth was 19% and we reported a healthy combined ratio of 89.3. All lines were profitable with the exception of Property, where catastrophic weather loss is added 30.6 points to the combined ratio. Policies in force growth continues to be strong at 12%. And I'm most excited to report that we pass the milestones of 17 million Personal Auto PIFs, 5 million special line PIFs, and 25 million company-wide PIFs during the first quarter. I also want to point out that this is the first time since the second quarter of 2004, that we reported double digit growth in personal auto, special lines and commercial lines policies in force. We couldn't be proud of that so many people trust Progressive to protect some of their most important assets. I’d like to take some time to address the effects that pandemic will have on our year-over-year comparative results for the next several months. March was the first month where we saw the effect of the pandemic in our previous year's results.
So, it feels like a good time to give some further insight into our March, 2021 results. And to remind everyone of the actions that we took in 2020 that could affect our year-over-year comparisons.
This quarter, we reported 14% new app growth in Personal Lines and 29% new app growth in Commercial Lines. The year-over-year growth reflects two items: the effect of the stimulus package and the denominator that includes the onset of the pandemic in which shopping, virtually stalled. Even considering the effects of that pandemic growth is robust. We've often said that PIF growth is our preferred measure of growth. This is a great example, why since the denominator was only nominally affected by dependent. Last year's new business metrics continued to be affected by the pandemic well into the summer of 2020.
So not always negatively. In mid-April, 2020, the first wave of stimulus checks, were released which restarted new business shopping.
We expect the uptick in shopping last year will affect our second quarter, 2021 year-over-year, new business growth. Also starting in April of last year, we took actions to support our customers, including our Apron Relief Program, which we believe will have an impact on many key metrics, including our expense ratio. At the end of April and May of 2020, our personal auto customers received monthly premium credits of 20%, which provided substantial financial assistance to our customers, but also increased our expense ratio.
In addition, as part of the Apron Relief Program, we initiated payment and billing leniency, which temporarily increased our bad debt expense, but also increased our positive retention. Both, policy enforced counts and retention metrics, were affected by billing leniency. In Commercial Lines, our TNC business saw a sudden and dramatic decrease in miles driven and estimated future miles to be driven in March of 2020, which contributed to the significant Commercial Lines, net premiums written increase in March of 2021, as noted in our March release. Miles driven in those premiums slowly recovered over the course of 2020, so we anticipate the effect on the denominator will decrease over the remainder of 2021.
Our property results continue to be rocked by catastrophic losses. In the first quarter, which is normally a relatively quiet quarter for cat losses, property business suffered significant losses. Further the hail storms in Texas and Oklahoma that occurred in late April appear to be another large event.
While it's too early to assess our ultimate exposure, I'll take this opportunity to remind everyone that we have an $80 million retention threshold from a single storm under our occurrence excess of loss reinsurance program. We'll more details on the late April events and our April release, which is currently scheduled for May 19. I'd also like to take a moment to thank everyone who participated in the perception study we commissioned at the beginning of the year. It was encouraging to see all the positive comments we received and it was helpful to receive feedback on ways we can improve. One opportunity that we heard loud and clear was a desire to return to the quarterly call format we had before the pandemic. One in which senior managers from around the organization will present on various aspects of the business. We intend to return to this format during at least two of the calls each year, starting with the August call, where we will highlight commercial lines.
Looking forward into the rest of the 2021, I'm filled with a sense of optimism.
While the pandemic is far from over and we still have many challenges ahead of us, I think, pride in the strength of our business, the resilience of our people and have confidence that the plans we have in place will likely continue to deliver great results in the coming quarters. Thank you. And I'm ready to take the first question Tamara.