Stax (formerly Fattmerchant)
- Stax uses subscription pricing: you pay a flat monthly fee ($99-199) and only pay interchange + a small per-transaction fee (no percentage markup)
- This saves money at $8K+/month in volume compared to flat-rate processors like Stripe/Square, and the savings grow with volume
- Stax includes invoicing, a virtual terminal, analytics, and basic fraud tools in the subscription
- The main limitation: you pay the monthly fee even in slow months, so it's a bad fit for seasonal or very low-volume businesses
Stax is built on a different pricing model than most processors. Instead of taking a percentage of every transaction, Stax charges a monthly subscription fee and passes interchange through at cost with no percentage markup. For businesses doing $8K+/month, this is usually cheaper than flat-rate pricing.
On this page
When to Use Stax
You should use Stax if:
- You process $8K+/month consistently (the monthly fee needs volume to justify itself)
- You want transparent interchange-plus pricing without calculating markup percentages
- You value predictable monthly costs (fixed subscription vs. variable percentage)
- You sell higher-ticket items (the savings per transaction are larger)
- You want invoicing, virtual terminal, and analytics bundled in
Skip Stax if:
- You process under $5K/month (monthly fee eats the savings)
- Your volume is highly seasonal or unpredictable
- You need advanced developer tools or API customization (Stripe is better)
- You're primarily card-present retail and want a full POS ecosystem (Square or Clover is better)
Pricing Breakdown
Subscription Plans
| Plan | Monthly Fee | Per-Transaction Fee | Best For |
|---|---|---|---|
| Growth | $99/month | IC + 8 cents (CP), IC + 15 cents (CNP) | $8K-$50K/month |
| Pro | $139/month | IC + 8 cents (CP), IC + 15 cents (CNP) | $50K-$150K/month |
| Ultimate | $199/month | IC + 8 cents (CP), IC + 15 cents (CNP) | $150K+/month |
IC = interchange cost, passed through at cost with zero percentage markup.
What's Included
All plans include:
- Virtual terminal
- Invoicing
- Customer vault (storing card data for repeat charges)
- Basic analytics dashboard
- ACH processing (0.5% + $0.25 per transaction, capped at $6)
- Standard funding (next-day funding available as paid add-on)
- Dedicated account manager (Pro and Ultimate)
The Math: Stax vs. Flat Rate
$20K/month volume, $50 average ticket (400 transactions), online:
| Stax (Growth) | Stripe | Square (Free plan) | |
|---|---|---|---|
| Interchange (avg 1.8%) | $360 | (bundled) | (bundled) |
| Processor fee | $99 + $60 (400 x $0.15) | $700 (2.9% + $0.30) | $780 (3.3% + $0.30) |
| Total | $519 | $700 | $780 |
| Savings | $181/month vs Stripe ($2,172/year) | - | - |
$5K/month volume, $25 average ticket (200 transactions), online:
| Stax (Growth) | Stripe | Square (Free plan) | |
|---|---|---|---|
| Interchange (avg 1.8%) | $90 | (bundled) | (bundled) |
| Processor fee | $99 + $30 (200 x $0.15) | $205 (2.9% + $0.30) | $225 (3.3% + $0.30) |
| Total | $219 | $205 | $225 |
| Savings | Stax is $14/month MORE expensive than Stripe | - | - |
Square Plus plan ($49/month) reduces online rate to 2.9% + $0.30, matching Stripe.
Breakeven point: roughly $8K/month for online transactions, $6K/month for card-present.
What Stax Does Well
1. True Interchange Passthrough
Stax passes interchange at cost with no markup percentage:
- You see exactly what Visa/Mastercard charges for each card type
- Debit cards cost you ~0.05% + $0.21 + $0.08 (Stax fee) instead of 2.9% + $0.30
- The savings are largest on regulated debit cards and basic credit cards
2. Predictable Monthly Cost
Your Stax subscription is fixed. Your only variable cost is interchange (which depends on card mix). This makes budgeting easier than percentage-based pricing where fees scale directly with revenue.
3. Built-in Business Tools
The subscription includes tools that other processors charge extra for:
- Invoicing with payment links
- Virtual terminal for phone orders
- Customer vault for repeat billing
- Reporting and analytics dashboard
- ACH processing at 0.5% + $0.25/transaction (capped at $6)
4. Dedicated Support
Unlike Stripe and Square (email-first), Stax provides:
- Phone support during business hours
- Dedicated account manager on Pro/Ultimate plans
- US-based support team
What Stax Does Poorly
1. Monthly Fee in Slow Months
If your volume drops, you still pay $99-199/month:
- Seasonal businesses get hurt in off-months
- Startups with inconsistent revenue may not break even
- No pause option for the subscription
2. Limited Developer Tools
Stax's API exists but is not in the same league as Stripe:
- Fewer integrations and plugins
- Less documentation
- No equivalent to Stripe Elements or Checkout
- Custom integration requires more effort
3. No Free Hardware
Unlike Square (free card reader), Stax charges for terminals:
- Card readers: $50-200
- Full terminals: $300-600
- Not a huge deal but adds to startup cost
4. Smaller Ecosystem
Stax has fewer integrations than Stripe or Square:
- Fewer e-commerce platform plugins
- Less third-party app support
- Growing but still smaller than competitors
Who Stax Is Best For
Perfect Fit
| Business Type | Why Stax Wins |
|---|---|
| Professional services ($10K+/mo) | High-ticket invoices, low transaction count, big savings per transaction |
| B2B businesses | Corporate cards have high interchange; Stax passes through without markup |
| Established e-commerce ($20K+/mo) | Consistent volume makes subscription model pay off |
| Medical/dental offices | High-ticket, low-volume, includes virtual terminal |
Poor Fit
| Business Type | Better Alternative |
|---|---|
| Startups/new businesses | Stripe or Square (no monthly fee) |
| Seasonal businesses | Square (no fee in off-months) |
| Under $5K/month | Any flat-rate processor |
| Developer-led SaaS | Stripe (better API) |
| Retail needing full POS | Square or Clover |
Stax vs. Similar Processors
| Stax | Payment Depot | Helcim | |
|---|---|---|---|
| Model | Subscription | Subscription | IC+ (no subscription) |
| Monthly fee | $99-199 | $59-99 | $0 |
| Per-transaction | IC + $0.08-0.15 | IC + $0.15 | IC + 0.40-0.50% + $0.08-$0.25 |
| Best at | $15K-200K/mo | $10K-100K/mo | $5K-100K/mo |
| Invoicing | Included | Limited | Included |
| API quality | Basic | Minimal | Basic |
The key difference: Stax and Payment Depot charge no percentage markup at all (just a flat per-transaction fee on top of interchange). Helcim charges a small percentage markup but has no monthly fee. At higher volumes, subscription models win; at lower volumes, Helcim's no-fee model wins.
Common Gotchas
1. Contract Length
Stax previously required annual contracts. Current plans are month-to-month, but verify before signing. Ask: "Can I cancel anytime with no early termination fee?"
2. Volume Requirements
Some Stax plans have minimum volume requirements. If your volume drops below the minimum, you may be moved to a different plan or charged differently. Clarify this upfront.
3. Interchange Categories
Since Stax passes interchange through, your effective rate depends heavily on your card mix. If most of your customers use premium rewards cards or corporate cards, interchange is higher. Check your card mix before assuming savings.
Test to Run
Stax savings calculator (before switching):
- Get your current processor statement
- Find: total volume, total transactions, total fees
- Calculate current effective rate:
fees / volume - Estimate Stax cost:
$99 + (transactions x $0.15) + (volume x average interchange rate) - Average interchange is roughly 1.8% for online, 1.5% for card-present
- Compare: Is Stax at least $50/month cheaper? If yes, worth switching
Success criteria: Stax saves you $600+/year after accounting for the monthly fee.
Next Steps
Considering Stax?
- Run the savings calculator above with your actual numbers
- Make sure your monthly volume is consistently above $8K
- Compare with Helcim (similar savings, no monthly fee)
Already on Stax?
- Check if you're on the right plan tier for your volume
- Review your card mix - are you getting the interchange savings you expected?
- Compare your effective rate to benchmarks
See Also
- Helcim - IC+ without monthly fee
- Processor Comparison - Full comparison table
- Understanding Fees - How interchange works
- Interchange Reference - Interchange rate tables