The $40 sale that shows the problem
Take one $40 sale at your counter. On Square's Free plan, that sale costs you $1.19 in processing fees — 2.6% plus 15 cents. Now run 250 sales a month — 70% in person, 30% online, $40 each — and you've handed over $329.75 for the right to accept your own customers' money. The same 250 sales through an interchange-plus processor cost $263.25. Same products, same customers, $798 a year apart.
That gap is the whole reason flat-rate versus interchange-plus matters. Flat-rate is simple: one percentage, easy to quote, easy to budget. Interchange-plus passes through the card networks' wholesale cost and adds a thin, published markup — cheaper in most cases, harder to explain at a glance. Below, every rate is a published 2026 figure, every monthly total is worked out from stated assumptions, and every crossover point is calculated, not guessed.
By the Small Business Tool Lab editorial team · October 1, 2026 · 9 min read
The four processors in this comparison
These are the four names that come up most when small retailers shop for processing, and each one represents a different pricing philosophy. Square and Stripe charge flat rates — one bundled percentage per transaction type. Helcim charges interchange-plus — wholesale cost plus a published margin. Stax charges a monthly subscription and passes interchange through with no percentage markup at all, adding only a few cents per transaction.
| Processor | Pricing model | In-person rate | Online rate | Monthly fee | Contract |
|---|---|---|---|---|---|
| Square (Free plan) | Flat-rate | 2.6% + 15¢ | 3.3% + 30¢ | $0 | Month-to-month |
| Stripe (standard) | Flat-rate | 2.7% + 5¢ (Terminal) | 2.9% + 30¢ | $0 | Month-to-month |
| Helcim | Interchange-plus | Interchange + 0.40% + 8¢ | Interchange + 0.50% + 25¢ | $0 | Month-to-month |
| Stax | Subscription + interchange | Interchange + 8¢ | Interchange + 15¢ | $99–$199+ | Month-to-month |
All rates above are published figures verified as of October 1, 2026. Helcim's published markups shown are for merchants processing up to $50,000 a month; its markups drop automatically at higher volumes. Stax's subscription is tiered by annual volume: $99 a month up to $150,000 a year, $139 a month from $150,000 to $250,000, and $199 or more a month above $250,000. Square also sells Plus ($49 a month) and Premium ($149 a month) plans that lower the rates — those matter later in the crossover section.
The assumptions behind every number below
Comparison tables are only as honest as their assumptions, so here are all of ours, stated up front. If your business looks different, the method still works — swap in your own numbers and follow the same steps.
- Average ticket: $40.
- Channel split: 70% in-person (swiped, dipped, tapped), 30% online or card-not-present.
- Interchange + network assessment base: 1.80% in person, 2.05% online. These are blended estimates for a typical retail card mix — mostly standard consumer credit and debit cards, no corporate or rewards-heavy skew.
- No international cards, no surcharging, no keyed-entry-heavy mix. US pricing only.
- Transaction counts follow from the ticket size: $10K means 250 transactions (175 in-person, 75 online); $25K means 625 (437 in-person, 188 online); $50K means 1,250 (875 in-person, 375 online).
- Helcim and Stax totals use each provider's published tier for that volume. Stax sits on the $99 tier at $10K a month ($120K a year) and the $199 tier at $25K and $50K a month. Helcim's automatic volume-discount tier is applied in the $50K scenario; it takes effect above $50,000 a month on a three-month average, so a store sitting right at $50K would still be on the standard tier.
At $10,000 a month: 250 transactions
This is the classic early-stage retail picture — a shop doing about $330 a day in card sales. Watch how the fixed monthly fee changes the story at this size.
| Processor | In-person cost | Online cost | Monthly fee | Total | Effective rate |
|---|---|---|---|---|---|
| Square | $208.25 | $121.50 | $0 | $329.75 | 3.30% |
| Stripe | $197.75 | $109.50 | $0 | $307.25 | 3.07% |
| Helcim | $168.00 | $95.25 | $0 | $263.25 | 2.63% |
| Stax | $140.00 | $72.75 | $99.00 | $311.75 | 3.12% |
Winner at $10K: Helcim at $263.25. It beats Square by $66.50 a month ($798 a year) and beats Stripe by $44 a month ($528 a year). Stax has the lowest per-transaction cost of all four — but its $99 subscription eats the savings at this volume, leaving it $4.50 more expensive than Stripe.
Two things worth noticing. First, Stripe beats Square Free everywhere in this mix: 2.7% + 5¢ in person undercuts 2.6% + 15¢ on a $40 ticket, and 2.9% + 30¢ online undercuts Square's 3.3% + 30¢. Second, Stax's problem at $10K is purely the subscription. That flips fast as volume grows.
At $25,000 a month: 625 transactions
Now the shop is doing real volume — roughly $830 a day. The subscription models start pulling away from flat-rate.
| Processor | In-person cost | Online cost | Monthly fee | Total | Effective rate |
|---|---|---|---|---|---|
| Square | $520.03 | $304.56 | $0 | $824.59 | 3.30% |
| Stripe | $493.81 | $274.48 | $0 | $768.29 | 3.07% |
| Helcim | $419.52 | $238.76 | $0 | $658.28 | 2.63% |
| Stax | $349.60 | $182.36 | $199.00 | $730.96 | 2.92% |
Winner at $25K: Helcim at $658.28. It saves $166.31 a month versus Square ($1,996 a year) and $110.01 a month versus Stripe ($1,320 a year). Stax has climbed to second place on pure transaction cost — but the jump to the $199 subscription tier at $250K in annual volume keeps it $72.68 a month behind Helcim.
Notice Stax's tier jump. At $25K a month you're processing $300K a year, which pushes you past Stax's $250K annual threshold into the $199 tier. The tier structure is the price of Stax's 0% markup: the subscription does the work that a percentage markup does for Helcim. That design choice is exactly what creates the crossover at the next volume level.
At $50,000 a month: 1,250 transactions
At $50K the ranking changes, and two things happen at once: Helcim's automatic volume discount kicks in, and Stax's per-transaction cost finally outweighs its subscription.
| Processor | In-person cost | Online cost | Monthly fee | Total | Effective rate |
|---|---|---|---|---|---|
| Square | $1,041.25 | $607.50 | $0 | $1,648.75 | 3.30% |
| Stripe | $988.75 | $547.50 | $0 | $1,536.25 | 3.07% |
| Helcim* | $813.75 | $450.00 | $0 | $1,263.75 | 2.53% |
| Stax | $700.00 | $363.75 | $199.00 | $1,262.75 | 2.53% |
*Helcim's volume-discount tier (interchange + 0.35% + 7¢ in person, interchange + 0.45% + 20¢ online) applies above $50,000 a month on a three-month average, and this row assumes you have crossed it. At the standard tier the $50K total would be $1,316.25 — $53.50 more than Stax.
Winner at $50K: effectively a tie once Helcim's discount applies. Stax costs $1,262.75 and Helcim costs $1,263.75 — one dollar apart. Both save roughly $386 a month ($4,632 a year) versus Square and about $273.50 a month ($3,282 a year) versus Stripe. Below Helcim's discount threshold, Stax leads by $53.50 a month. Either way, at this volume pick on features, hardware, and support — not on price.
The five crossover points
The tables show three snapshots. The crossovers tell you where to move — and where to sit still.
| Switch | Crossover volume | What it means for you |
|---|---|---|
| Square Free → Helcim | No crossover — Helcim wins from the first dollar | In this retail mix, interchange-plus undercuts Square's flat rate at every volume. If you're on Square Free for the simplicity, you're paying for it. |
| Square Free → Stripe | No crossover — Stripe wins at every volume | Stripe's lower in-person and online rates beat Square Free across the board here. But note the trade-off: Stripe is online-first, and its in-person rate needs Stripe Terminal hardware. |
| Square Free → Square Plus ($49/mo) | About $26,000/month | Plus cuts in-person to 2.5% + 15¢ and online to 2.9% + 30¢. The $49 fee pays for itself above roughly $26K in a 70/30 mix. Below that, stay on Free. |
| Stripe → Stax ($99 tier) | About $10,500/month | Stax's near-zero per-transaction cost overtakes Stripe just above $10K. But the $99 tier caps at $150K a year ($12.5K a month) — a narrow window before the $139 tier moves the goalpost. |
| Helcim → Stax ($199 tier) | About $39,000–$50,000/month | On published standard tiers, Stax pulls ahead near $39K. But Helcim's automatic volume discount narrows the gap, and just above $50K the two land within $1 of each other. Past that point, compare features instead of fees. |
One honest caveat: these crossovers shift with your mix. A debit-heavy store favors Helcim and Stax even earlier, because interchange-plus passes the regulated debit cap straight to you while flat-rate keeps the difference. A keyed-entry-heavy business — phone orders, invoices typed in by hand — narrows the gap, because keyed rates run higher everywhere: 3.5% + 15¢ on Square, interchange + 0.50% + 25¢ on Helcim.
Hidden fees to check before you sign
The rate tables cover the headline math. These are the line items that ambush owners on the statement — each provider publishes the following terms as of October 1, 2026, but every one deserves a direct question before you commit.
- Monthly fees and tier timing. Square: $0 / $49 / $149 by plan. Stripe: $0. Helcim: $0 — its volume discounts apply automatically on a three-month average, no phone call needed. Stax: $99 to $199+ by annual volume, so crossing $150K or $250K a year moves your subscription up. Ask Stax exactly when the tier change takes effect.
- PCI compliance fees. Helcim charges no PCI fee. Stax includes PCI compliance in the subscription. Square and Stripe carry no separate PCI fee. If any quote you receive adds a monthly "PCI" or "compliance" line, that's a markup wearing a costume.
- Cancellation terms. All four are month-to-month with no published cancellation fee. Stax asks for 30 days' notice. Helcim's standard terms route termination through a support call during business hours — confirm what that process looks like before you need it.
- Chargeback and dispute fees. Square charges $0 per dispute — a real advantage if your business sees frequent chargebacks. Stripe charges $15. Helcim charges $15 but refunds it if you win the dispute. Stax does not publish its chargeback fee prominently; get the number in writing before signing.
- Hardware. Square ships a free basic card reader and sells a full POS lineup. Stripe's in-person rate requires Stripe Terminal hardware, purchased separately. Helcim's card reader is $199 and its smart terminal $349, with financing available. Stax is equipment-agnostic and will reprogram compatible existing terminals free — meaningful if you already own hardware.
- International cards. Stripe adds 1.5% on international cards plus 1% for currency conversion. If tourists or cross-border buyers are a real share of your sales, model them separately — none of the tables above include them.
- Statement minimums and batch fees. None of these four publish a monthly minimum or batch fee. If your agreement shows either one, treat it as a red flag and ask for it to be removed.
Frequently asked questions
Is interchange-plus always cheaper than flat-rate?
Not always, but in our modeled retail mix it usually is. Helcim's interchange-plus pricing beats Square Free from the first dollar, while Stax's subscription-plus-interchange model only overtakes flat-rate once you pass roughly $8,500 to $10,500 a month — its $99 subscription makes it slightly more expensive than Stripe below about $10,500. Very low volume, tiny tickets, or a keyed-entry-heavy mix can all tilt the math back toward flat-rate. Run your own statements through the method in the checklist instead of trusting a rule of thumb.
How do I calculate my real effective processing rate?
Take two or three recent processor statements. Divide total fees paid by total card sales, then multiply by 100. That percentage is your effective rate — the only number that lets you compare processors honestly, because it captures every markup, per-transaction fee, and monthly charge at once. Compare it against the effective-rate column in the tables above, not against anyone's advertised headline rate.
Your 10-step selection checklist
Work this list in order. It takes one afternoon and a calculator.
- Pull your last three statements. Write down monthly card volume, your in-person versus online split, and your average ticket.
- Compute your effective rate. Total fees divided by total card volume. If it's above 3%, you're almost certainly overpaying.
- Match your volume to the tables above. Find the cheapest row for a mix like yours — that's your target.
- Find your nearest crossover. Within $5,000 a month of a switch point? That decides whether you move now or wait for the next tier.
- Price the hardware you actually need. A free reader that can't do what your counter needs isn't free — compare the full hardware bill, not just the reader.
- Read the cancellation clause before the rate sheet. Month-to-month with no fee is the standard here. Anything stricter is negotiable.
- Ask about the chargeback fee and the PCI fee by name. Get both answers in writing, especially from providers that don't publish them.
- Check the tier triggers. Stax's $150K and $250K annual thresholds, Helcim's three-month average rule — know exactly when your pricing changes.
- Model your debit share. Regulated debit interchange is capped, and interchange-plus passes that saving to you. Flat-rate keeps the difference.
- Re-run this math every 12 months — or after any 30% swing in volume. The cheapest processor at $10K is not the cheapest at $50K, as the tables prove.
Start with step one today: pull a statement and compute your effective rate. If the number surprises you, the tables above already show you where the money goes — and the checklist shows you how to keep it.
This guide is for general information only and is not financial advice. Processor rates, fees, and plan tiers change frequently — every figure above reflects published pricing verified as of October 1, 2026, combined with the modeled assumptions disclosed in this article. Confirm current terms with each provider before you sign or switch.