TL;DR
For professional services firms processing $25K to $5M monthly, Helcim wins on transparent interchange-plus pricing with no contract. Stax pulls ahead above roughly $80K monthly volume because the $99 subscription stops being a tax and starts being a discount. Payment Depot competes with Stax when transaction count is high and tickets are moderate. Stripe earns its keep only if your billing system needs API work. Skip PayPal Standard on B2B invoices over $1,000; the rate jumps to 3.49% plus $0.49.
How we ranked
Professional services has a card mix and ticket profile that punishes flat-rate processors more than retail does. A $2,500 retainer at 2.9% plus $0.30 costs $72.80. The same charge at interchange-plus on a Visa rewards card costs around $48. That gap is the reason this list exists.
We weighted six criteria:
- Effective rate at $100K monthly volume. Modeled on a $1,200 average ticket and 70% card-not-present mix typical for law firms, agencies, and accounting practices.
- Level 2 and Level 3 data support. Commercial cards qualify for lower interchange when you pass invoice number, tax amount, and line items. Savings run 0.50 to 0.80 percentage points per transaction, per the Visa Interchange Schedule.
- Recurring billing and ACH. Retainers, monthly fees, and trust deposits need both.
- Trust account handling. Legal firms need IOLTA-compliant separation of fees from client funds.
- Contract length and early termination fees. Anything over 12 months with a real ETF gets penalized.
- Settlement speed. 1 to 2 business days is the floor.
At a glance
| Provider | Headline pricing | Contract | Settlement | Best for | Watch out for |
|---|---|---|---|---|---|
| Helcim | IC + 0.50% + $0.25 online; IC + 0.40% + $0.08 in-person | No contract | 2 days | $25K to $80K monthly | No 24/7 phone support |
| Stax | $99/mo + IC + $0.18 online; + $0.08 in-person | Month to month | 2 days | $80K+ monthly | Subscription dead weight under $50K |
| Payment Depot | $79 to $199/mo + IC + $0.05 to $0.15 | Month to month | 2 days | High transaction count | Pricing varies by tier and rep |
| Stripe | 2.9% + $0.30 online; 2.7% + $0.05 in-person | No contract | 2 days | API-heavy billing | Flat rate punishes high tickets |
| Square | 2.9% + $0.30 online; 2.6% + $0.10 in-person | No contract | 1 day | Sub-$25K solo practices | 3.5% + $0.15 on keyed cards |
| PayPal | 3.49% + $0.49 Standard; 2.59% + $0.49 Advanced | No contract | 1 day | Consumer-facing checkout | Punitive B2B card-not-present pricing |
Helcim
Helcim publishes a straight interchange-plus rate: IC + 0.50% + $0.25 for online transactions and IC + 0.40% + $0.08 for in-person, per the Helcim pricing page. There is no monthly fee, no setup fee, and no contract.
On a typical professional services card mix (regulated Visa CPS plus commercial Visa Business, average ticket $1,200), the effective rate lands at roughly 2.30 to 2.45% for online charges. That is 0.45 to 0.60 percentage points below Stripe's flat rate. On $100K monthly volume, the savings sit between $450 and $600 per month, or $5,400 to $7,200 a year.
Helcim also discounts the markup automatically as volume rises. The published schedule cuts the percentage portion in tiers as you cross $25K, $50K, $100K, and $250K monthly.
Best for: firms between $25K and $80K monthly that want pricing they can verify on a statement. Avoid if: you need 24/7 phone support. Helcim covers business hours only.
Stax
Stax charges $99 per month plus interchange and a per-transaction fee of $0.08 in-person or $0.18 online (Stax pricing). There is no percentage markup on the swipe; you pay the network rate and a flat fee on top.
That structure flips at scale. At $50K monthly on the typical professional services card mix, Helcim still wins because the percentage markup is small. Cross $80K to $100K and Stax pulls ahead. At $250K monthly, the $99 subscription works out to under 0.04% effective overhead, less than half of Helcim's 0.50%.
Stax supports Level 2 and Level 3 data through its gateway. B2B firms processing commercial card payments will see additional 0.50 to 0.80 percentage points of savings on qualifying transactions, per the Mastercard Interchange Rates and Criteria.
Best for: firms over $80K monthly with a steady book of recurring invoices and corporate-card exposure. Avoid if: monthly volume sits below $50K. The $99 fee burns through the savings.
Payment Depot
Payment Depot uses the same subscription model as Stax with tighter per-transaction pricing. Membership runs $79 to $199 per month depending on tier, plus interchange and $0.05 to $0.15 per transaction (Payment Depot pricing).
The math gets interesting at high transaction counts and moderate tickets. Picture a tax practice running 600 monthly card-not-present transactions at $350 average ticket. Stax bills $99 plus 600 transactions at $0.18 each, which is $207. Payment Depot at the $79 tier with $0.08 per transaction costs $127. That $80 monthly gap compounds across the year.
The catch is that the wholesale model only pays off if you process enough volume to absorb the membership. Below $25K monthly, the $79 dead weight matches what you would save by switching.
Best for: firms with high transaction counts where the per-item fee dominates. Avoid if: volume sits below $25K monthly.
Stripe
Stripe charges 2.9% plus $0.30 online and 2.7% plus $0.05 in-person on its flat-rate plan, per the Stripe pricing page. There is no monthly fee. Volume discounts and interchange-plus are available only by direct negotiation.
On the $100K monthly model, Stripe runs about $2,900 in processing fees. The same volume on Helcim runs roughly $2,350. The gap is real, but Stripe earns its premium in two cases: when your billing logic is genuinely complex (usage-based pricing, multi-currency, nested subscriptions) or when you need a developer to ship a custom checkout in a week.
Stripe supports Level 2 data automatically and Level 3 through the API. Stripe Tax, Billing, and Revenue Recognition each carry separate per-charge or percentage fees. Read the line-item pricing before turning on add-ons.
Best for: firms with engineering resources building a custom client portal or invoicing flow. Avoid if: a standard hosted invoice would do the job and your average ticket exceeds $500.
Square
Square charges 2.6% plus $0.10 in-person, 2.9% plus $0.30 for online invoices, and 3.5% plus $0.15 for manually keyed cards, per the Square pricing page. The keyed-in rate is what hurts professional services firms; a card read off a paper form or recited over the phone runs through that 3.5% lane.
Square's free invoicing tool and same-day setup make it useful for solo practitioners taking $5K to $20K monthly. Above $25K, the cost differential against Helcim starts running $200 to $500 per month even before counting keyed transactions.
Square supports Level 2 data on its eCommerce API for commercial cards but not Level 3. Recurring billing and ACH are available. The ACH rate is 1% with a $1 minimum, less competitive than Helcim's flat $0.50 ACH fee on most invoice sizes.
Best for: solo practitioners under $25K monthly who want one app for invoicing, scheduling, and card acceptance. Avoid if: a meaningful share of your charges are keyed.
PayPal
PayPal charges 3.49% plus $0.49 on standard card transactions, 2.59% plus $0.49 on the Advanced Checkout tier, and 2.29% plus $0.09 in-person, per the PayPal business fees page. The $0.49 transaction floor is the largest in this comparison.
The brand has consumer trust at checkout, and the PayPal button still lifts conversion on B2C transactions. The problem for professional services is the average ticket. A $2,500 retainer on PayPal Standard costs $87.74 in fees. The same charge through Helcim runs around $25.
PayPal's Pay Later and invoicing tools have improved, but the rate structure has not. Most law firms, agencies, and accounting practices we model end up paying $400 to $800 more per month on PayPal than on any interchange-plus competitor.
Best for: low-ticket consumer add-ons inside a larger checkout. Avoid if: invoices average over $500.
Verdict
For professional services firms processing $25K to $80K monthly, Helcim is the cleanest choice. Published interchange-plus pricing, no contract, automatic volume tiering, and tools that handle invoices, recurring billing, and ACH. Savings against a flat-rate processor like Stripe or Square run $5,400 to $7,200 a year at $100K volume on a typical card mix.
Above $80K monthly, run the math on Stax. The $99 subscription becomes a rounding error at $250K, and the Level 3 support pulls down interchange on B2B cards. Payment Depot is the alternative when transaction count dominates dollar volume.
Stripe earns its premium when engineering work is required. PayPal earns it almost never. Federal Reserve data shows card-not-present interchange centered well below most flat rates, per the Federal Reserve payments program. Anything you pay above interchange is the processor markup, and it should be visible on the statement.
