Reconciliations of these non-GAAP financial measures to the most directly comparable GAAP measures are available in the recent earnings press release available on the company's website. Q3 revenue of $104.6 million was in line with our expectations, representing 10% reported year-over-year growth. We outperformed internal profitability expectations, delivering adjusted EBITDA of $35.2 million, representing a margin of 34%. Our team remains focused on investing for growth, with R&D up 24% versus the same period a year ago and increasing to 10% of revenue from 9% in the prior year period.
On the other hand, Q3 bookings of $96.6 million came in below our expectations, representing growth of 1%. Taking this into account, we are narrowing our revenue guidance to $415 million-$420 million, which we believe reflects the most likely range of outcomes for the year based on our performance to date. We continue to see pockets of outperformance throughout our portfolio, including our Simcyp PBPK software and our QSP services. Customers are adopting biosimulation solutions for use in dosing, efficacy, and toxicity analysis, and using the technology earlier as we expand our software capabilities into discovery and preclinical.
Since our IPO, we have seen a significant increase in both the number of customers using our products and services as well as the wallet share of Certara within larger organizations. We closed the ChemAxon acquisition a year ago in early October of 2024, which gave Certara an established product suite in discovery with synergistic capabilities relative to Simcyp. Elsewhere, our services group has grown preclinical work in QSP, especially since the FDA's guidance promoting the use of new approach methodologies. Software revenue of $43.8 million grew 22% on a reported basis and 6% organically, led by strong growth from Simcyp, in addition to $5.6 million of contribution from ChemAxon.