Flatpay vs SumUp vs Square: Which Card Reader Is Best for Your Business?

Every year, thousands of UK small businesses choose a payment provider without a clear picture of what separates one from another. Flatpay, SumUp, and Square are three of the most visible options in 2026, and all three position themselves as affordable, transparent alternatives to traditional merchant services. But they are built on fundamentally different foundations.

Flatpay is an in-person specialist. SumUp is a financial platform. Square is a full commerce ecosystem. Choosing between them is not about the lowest number on a fee schedule — it is about understanding which platform fits the shape of your business.

Every data point in this comparison comes from the providers’ own UK websites. All facts are verified. Where a provider does not publish information, a dash is shown and we direct you to the provider directly.

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Why Compare All Three?

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Master Comparison Table

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The Three Providers: Who They Are

Flatpay

Founded in 2022 in Copenhagen, Flatpay is the youngest of the three. Its proposition: one flat rate for every card, no monthly fee, and a real person to install everything. Backed by Dawn Capital, Seed Capital, AVP, and Smash Capital, Flatpay has grown to over 70,000 merchants across six European markets. Its UK base is in White City, London.

Flatpay is a payment processing company only. It does not offer a business bank account, invoicing, online selling, loyalty tools, or booking systems. Flatpay ApS is registered at Companies House (BR027644) but does not appear to hold FCA authorisation. Verify at register.fca.org.uk before signing up.

SumUp

Founded in 2012, SumUp is the most established of the three in Europe. SumUp Payments Limited is FCA authorised under the Electronic Money Regulations 2011 (FRN 900700). It serves over 4 million merchants worldwide and processes billions of pounds monthly.

SumUp has evolved from a card reader company into a financial platform. Its free Business Account integrates directly with payment tools. Next-day payouts arrive even on weekends and bank holidays. Making Tax Digital support, in partnership with Sage, is built into the dashboard — HMRC-recognised software for quarterly filing. SumUp charges a £10 non-refundable fee per chargeback dispute.

Square

Founded in 2009 in San Francisco, Square is owned by Block, Inc. (NYSE: SQ) and is the largest of the three by scale. In the UK it operates through Squareup Europe Ltd, FCA authorised (FRN 900846). Square’s product suite is the most comprehensive: dedicated POS for restaurants, retail, and appointments; an online store; invoicing; virtual terminals; payment links; Clearpay BNPL; loyalty; marketing; team management; and a full developer API. Square charges £0 for chargebacks.

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Fee Comparison

Rate Analysis

In-person rate: Flatpay’s Terminal at 1.49% is the lowest standard rate — 0.20 points cheaper than SumUp and 0.26 points cheaper than Square. On £10,000 of monthly card sales that is a saving of £20 and £26 respectively before any monthly fee is factored in.

SumUp Payments Plus changes the picture at volume. At £3,000 or more per month, the 0.99% rate under Payments Plus (£19/month) makes SumUp the cheapest option. At £5,000/month: SumUp costs approximately £68.50 versus Flatpay’s £74.50 and Square’s £87.50. The crossover is approximately £2,500/month.

Square’s Plus plan does not reduce the transaction rate — it adds software features. Square does not compete on transaction rate at any volume unless on the Premium plan with custom pricing at £200,000+ annual turnover.

Online payments: Only SumUp and Square offer these. Square’s 1.4% + 25p for UK cards is significantly cheaper than SumUp’s 2.50% for most transaction sizes. For a £50 transaction: Square charges 95p, SumUp charges £1.25.

Chargeback Fees — An Important Distinction

Square: £0. SumUp: £10 per dispute (non-refundable, deducted whether or not the merchant wins). Flatpay: not published on its UK website. For businesses in sectors prone to disputes — e-commerce, high-value retail, subscription services — this difference is commercially meaningful.

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Hardware

SumUp and Square both use the self-install model — hardware ships in a box and you set it up yourself. Flatpay takes the opposite approach: every product comes with a dedicated on-site installation. This removes risk of misconfiguration and reduces burden on non-technical staff — a genuine advantage for businesses upgrading from traditional till systems.

Square has the strongest hardware guarantee: 2-year warranty on all devices and free 30-day returns. SumUp offers 1-year warranty and 30-day money-back. Flatpay does not publish warranty or returns terms on its UK website.

Square offers interest-free hardware instalment plans from 3 to 12 months on purchases of £29 to £3,000. Neither SumUp nor Flatpay offers instalment hardware plans. Tap to Pay is available on both SumUp and Square at no cost — Flatpay does not offer it.

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Software & Digital Features

This is where the three providers diverge most sharply. Flatpay is a payments-only platform. SumUp and Square both offer comprehensive digital ecosystems — but with different emphases.

Flatpay: Focused on In-Person

Flatpay’s software covers what you need to take payments and manage basic sales. The Merchant Portal provides real-time reporting and automatic accounting uploads. The mPOS and POS products add table management, Dine-in/Dine-out mode, discounts, split billing, and optional kitchen printing. That is the full extent of Flatpay’s digital offering. Businesses needing invoicing, payment links, online selling, booking tools, loyalty, or marketing will need separate third-party software.

SumUp: Financial Platform with MTD Focus

SumUp’s strength is financial management. The free Business Account with Mastercard provides merchants a real UK current account — account number, sort code, instant transfers, automated expense categorisation, and next-day payouts even on weekends. The Making Tax Digital integration, powered by Sage and HMRC-recognised, is a unique feature among the three providers. For self-employed merchants now filing quarterly under MTD for Income Tax (rolled out April 2026), this built-in compliance tool removes the need for separate accounting software.

Square: The Complete Commerce Platform

Square’s software depth is unmatched in this comparison. Square for Restaurants is a full-service hospitality POS with table management, kitchen displays, course routing, and delivery integration. Square for Retail offers advanced inventory management, multi-location syncing, and barcode scanning. Square Appointments is a dedicated booking system with automated SMS reminders, waitlists, and online booking pages.

Beyond vertical POS, Square offers free invoicing, free payment links, a virtual terminal, an online store (free, with custom domain from £20/month), loyalty (from £25/month), marketing tools (from £9/month), team management, Kitchen Display Systems (from £15/device/month), and a full developer API with an extensive App Marketplace. Clearpay Buy Now Pay Later allows customers to pay in four interest-free instalments — the merchant receives full payment immediately at 6% + 30p per transaction.

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Security, Regulation & Fund Protection

SumUp: FCA Authorised, Transparent

SumUp Payments Limited is FCA authorised (FRN 900700) under the Electronic Money Regulations 2011. Customer funds are held in dedicated segregated accounts. Not FSCS-protected, but EMR safeguarding provides strong ring-fencing. PCI DSS compliance confirmed. 3D Secure on business account card. Biometric login. Chargeback fee: £10 per dispute, non-refundable.

Square: FCA Authorised, £0 Chargebacks

Squareup Europe Ltd is FCA authorised (FRN 900846). Customer funds safeguarded in segregated accounts. PCI DSS compliant. End-to-end encrypted payments. Active fraud prevention built-in. £0 chargeback fee. 2-year hardware warranty. Account takeover protection on every account. Square Loans explicitly not FCA regulated — stated by Square.

Flatpay: Regulatory Position

Flatpay ApS is a Danish company registered at Companies House as a UK branch (BR027644). It does not appear to hold FCA authorisation. All card processing requires PCI DSS compliance and encrypted transactions as standard network requirements — Flatpay’s processing meets these. However, businesses requiring confirmed FCA authorisation should verify at register.fca.org.uk before committing.

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Business Funding

Flatpay Capital

Merchant cash advance for existing Flatpay merchants. Provided by Flatpay Financial Services A/S, powered by Liberis. Pre-approved based on card sales history. 60% of merchants funded within 3 business days (September 2025 data). Subject to underwriting. Minimum monthly repayment applies.

SumUp Cash Advance

Invite-only for existing SumUp merchants. Fixed fee upfront, no interest. Funds within 2 working days. Repayment: set percentage of daily card sales, no deduction on zero-sale days. Early repayment at no extra charge. Commercial advance, not a regulated loan.

Square Loans

Invite-only for existing Square merchants (company or corporation structure only). Typical offer: £10,000 with a flat fee of £1,325 (representative APR 18.90%). Repayment: 17.25% of daily Square card sales. Maximum term 18 months. No credit checks, no interest, no late fees. Explicitly not FCA regulated — stated by Square on its UK website.

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Who Should Choose Each Provider?

Choose Flatpay if:

• You primarily take in-person payments and want the lowest standard flat rate — 1.49% on the Terminal
• You want professional on-site installation — a Flatpay specialist comes to your premises and sets everything up
• You run a hospitality business needing table management, Dine-in/Dine-out, and kitchen printing without a monthly software subscription
• You do not need invoicing, payment links, online selling, or appointment bookings

Choose SumUp if:

• You want a free UK business bank account integrated with your payment tools — next-day payouts, a free Mastercard, instant free UK transfers
• You need Making Tax Digital compliance built into your financial dashboard, powered by Sage
• You process £3,000+ per month and want to bring your rate down to 0.99% with Payments Plus
• You run a beauty or service business needing appointment bookings, automated reminders, and loyalty tools
• You want clear FCA regulation and transparent fund safeguarding

Choose Square if:

• You need the most complete commerce platform — restaurant POS, retail inventory, appointment booking, online store, invoicing, and team management from one provider
• You sell online as well as in person and want the best online payment rate — 1.4% + 25p for UK cards
• You want the strongest hardware package: 2-year warranty, free 30-day returns, and interest-free instalment plans
• You value £0 chargeback fees and a well-documented security framework
• You need developer API access or App Marketplace integrations

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Final Verdict

For simplicity and in-person focus: Flatpay

If your business lives and dies by in-person card sales, you have no need for digital selling tools, and you want a real person to take care of setup — Flatpay’s 1.49% Terminal with on-site installation is a genuinely compelling option. The trade-off is the absence of digital tools and the lack of confirmed UK FCA authorisation, which should be verified at register.fca.org.uk before committing.

For financial management and UK compliance: SumUp

If you want one platform that handles payments, banking, invoicing, and tax compliance — and you want it to be clearly FCA regulated in the UK — SumUp is the strongest all-round financial platform of the three. The free Business Account, Making Tax Digital support, and Payments Plus at 0.99% for high-volume merchants make it the most financially comprehensive option. Note that SumUp charges £10 per chargeback dispute.

For complete commerce coverage: Square

If you are building a business that needs restaurant-grade POS, multi-channel retail tools, online booking, an online store, Clearpay BNPL, and a developer API — all from one platform — Square is in a different category from the other two. The 1.75% in-person rate is the highest of the three, but the ecosystem depth, the 2-year hardware warranty, and £0 chargeback fees make it the right answer for many growing businesses.

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PS: Still comparing options? For a deeper dive into any two providers, see our dedicated comparisons: Flatpay vs SumUp, Flatpay vs Square, and SumUp vs Square.