ACIW vs FISV: How ACI Worldwide and Fiserv Compare (2026)

Same yardstick, side by side (as of August 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: FISV 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 FISV 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 FISV 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

Fiserv is one of the largest payments and financial-technology companies in the world. It operates broadly in two areas: merchant solutions, where it processes card and digital payments for millions of businesses and runs the Clover point-of-sale and small-business platform, and financial solutions, where it provides core account processing, card issuing, digital banking, and related technology to banks and credit unions. Most of its revenue is recurring and transaction-based, tied to the volume of payments and accounts it processes, which gives the business a steady, infrastructure-like quality. Fiserv changed its listing to the Nasdaq and reinstated its original ticker symbol FISV (from FI) in November 2025.

Full FISV 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.
• FISV drivers: Recurring, transaction-based revenue; Clover platform growth.

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 FISV, the main risk is that Fiserv's growth is modest, so slowing organic revenue growth, margin pressure, or weaker free cash flow can disappoint investors, as the 2026 share weakness showed.

Growth-minded investors who believe the theme has years to run tend to accept the richer multiple for more upside; value-minded investors lean toward the cheaper forward earnings and steadier profile. Pick ACIW if you believe its drivers more; FISV 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 FISV 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.

FISV. Figures are approximate and tied to the asOf date; verify live numbers before acting. Fiserv is a profitable, cash-generative company, so an earnings multiple is meaningful, and the 2026 share weakness left some valuation metrics looking discounted versus its history. But the market's concern is the pace of organic growth, margins, and free-cash-flow recovery, so investors should weigh those trends and execution on internal initiatives rather than the multiple alone.

Headline figures (approximate, August 2026): ACIW shows market cap ~$5.9B, revenue (ttm) ~$1.79B, net income (ttm) ~$206M, eps (ttm) ~$1.98; FISV shows revenue (q1 2026) ~$5.03 billion, down about 2% year over year, adjusted eps (q1 2026) ~$1.79, beating expectations though down year over year, gaap eps (q1 2026) ~$1.07, 2026 guidance organic revenue growth ~1% to 3%; adjusted EPS ~$8.00 to $8.30 (reaffirmed).

ACIW and FISV 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 FISV exposure against your real portfolio. It is not an investment adviser.