ACIW vs PAY: Which Is the Better Buy in 2026?

Same yardstick, side by side (as of September 2026). Valuation lined up like this is most meaningful for two names in the same corner of the market, which these are. Figures are approximate; verify before investing.

Reading it: ACIW is the cheaper of the two on forward earnings, but cheaper is not the same as better. Pair the valuation with growth (how far the forward P/E sits below the trailing P/E) and risk (beta) before you decide.

The metrics above tell you which is the marginally better business. The bigger risk for most people is not picking the slightly worse stock, it is over-concentrating. ACIW and PAY share themes, so owning both, or adding either to what you already hold, can quietly push a large share of your portfolio into one bet.

This is the part a generic comparison page cannot answer, because it depends on what you own. Connect your brokerage and Walnut shows your real, combined ACIW and PAY exposure, flags overlap with your existing positions, and tells you if adding one would tip you past a concentration you are comfortable with, read-only by default, with your login staying at your broker. Walnut is not an investment adviser.

ACI Worldwide, Inc. builds the software that moves and manages payments behind the scenes. Founded in 1975 and headquartered in Florida, the company sells payment hubs and real-time payment engines to banks and processors, authorization and orchestration software to large merchants, machine-learning fraud detection across both, and, through its Biller segment, electronic billing and digital collections for utilities, insurers, telecoms, healthcare providers and government agencies. After a 2025 reorganization the business reports in two segments: Payment Software (the former banking and merchant units combined) and Biller. Its customers are institutional and sticky, deployments run for years, and a meaningful share of revenue comes from outside the United States.

Full ACIW guide

Paymentus Holdings runs a cloud-native platform that lets billers (utilities, government agencies, insurers, telecoms, and financial institutions) accept and manage electronic bill payments across many channels, including web, mobile app, IVR phone, chat, SMS, and walk-in, all synchronized in real time. Its differentiator is a single-codebase platform and its Instant Payment Network (IPN), which links roughly 2,500-plus billers to high-traffic consumer endpoints such as PayPal, Amazon, and Walmart. Revenue comes from a mix of per-transaction fees, hosted subscription portals, and premium add-ons, producing recurring, sticky enterprise relationships with high retention.

Full PAY guide

Both fit overlapping themes, but they are not interchangeable. The useful comparison is which set of drivers and risks you want exposure to.

• ACIW drivers: Real-time payments modernization; The shift from license to subscription.
• PAY drivers: Structural shift to digital bill pay; Transaction volume and network effects.

A faster-growing, richer-valued name usually swings harder, so it suits a longer horizon and a higher tolerance for volatility; a steadier, more cash-generative business suits a more conservative or income-minded investor. The honest test is which set of risks you could hold through a drawdown: The single most persistent issue is revenue lumpiness: term license renewals concentrate in particular quarters, so reported growth and GAAP earnings can swing sharply on the timing of a handful of large bank contracts, and trailing-twelve-month net income of roughly $206 million was down about 24% even as revenue grew. For PAY, valuation is the primary risk: the shares trade at a premium multiple, so any deceleration in revenue growth or a guidance miss could compress the stock sharply.

Pick ACIW if you believe its drivers more; PAY if you believe its. Many investors hold both, but since they share themes, that is a concentrated bet, not diversification. Decide deliberately and check overlap. For the full detail, see the ACIW and PAY guides.

ACIW. The wide gap between the trailing multiple of roughly 29 times and the forward multiple of roughly 17 times reflects both the expected 2026 earnings recovery and the license-timing distortion in trailing GAAP results, so the trailing figure on its own overstates how expensive the shares look. Free cash flow was roughly $310 million in FY2025 against net debt of roughly $644 million, which is a comfortable coverage ratio for a software business. Second-quarter 2026 results were scheduled for August 6, 2026, with company guidance of roughly $420 million to $440 million of revenue and roughly $85 million to $95 million of adjusted EBITDA.

PAY. Paymentus grew fiscal 2025 revenue about 37% to roughly $1.2 billion and stayed profitable, then raised full-year 2026 guidance to about $1.425 billion to $1.440 billion after a record first quarter. At roughly $3 billion of market value against about $74 million of trailing net income, the trailing earnings multiple is high, reflecting expectations that rapid growth and margin expansion continue.

Headline figures (approximate, August 2026): ACIW shows market cap ~$5.9B, revenue (ttm) ~$1.79B, net income (ttm) ~$206M, eps (ttm) ~$1.98; PAY shows revenue (ttm) ~$1.28B, revenue growth (yoy) ~30%, net income (ttm) ~$74M, adjusted ebitda (2026e) ~$165M to $172M.

ACIW and PAY are related but distinct: same themes, different businesses and risks. Neither wins in the abstract; the right pick is whichever thesis you actually believe, sized so you are not over-concentrated in one theme. Walnut can show your combined ACIW and PAY exposure against your real portfolio. It is not an investment adviser.