Tools

37 free tools for payment fees, profitability, and payment engineering. Every tool is embeddable on your own site.

Payment fee calculators (5)

  • Stripe Fee Calculator

    Calculate exactly what Stripe charges on any payment — including international cards, currency conversion, and ACH — and what you should charge to receive a target amount.

  • PayPal Fee Calculator

    Calculate PayPal fees for every payment type — Checkout, card payments, QR, Goods & Services, Pay Later — including international surcharges, plus what to request to receive an exact amount.

  • Square Fee Calculator

    Work out exactly what Square charges per payment across online, in-person, and manually keyed transactions — and what to charge to net a target amount.

  • Credit Card Processing Fee Calculator

    Calculate the fee on any payment from your rate, or audit a monthly statement: your true effective rate and how it compares with Stripe, Square, and PayPal on the same volume.

  • Payment Processor Comparison

    Compare what Stripe, PayPal, Square, and Shopify Payments actually cost on your volume — enter your numbers, see ranked monthly and annual costs, effective rates, and where interchange-plus wins.

Profit & ad calculators (7)

  • ROAS Calculator

    Work out your return on ad spend from revenue and spend, or flip it around: the revenue you need to hit a target ROAS, and the max you can spend at your current revenue.

  • Breakeven ROAS Calculator

    Find the exact ROAS where your ads stop losing money, based on your AOV, product costs, shipping, and payment fees — with a profit table across ROAS levels.

  • Shopify Profit Calculator

    Calculate true profit per order on Shopify: plan-specific Shopify Payments rates, third-party gateway surcharges, product costs, shipping, and ad spend.

  • Break-Even Calculator

    Find how many units you must sell to cover fixed costs, your break-even revenue, and profit at different sales volumes — from price, variable cost, and fixed costs.

  • CAC & LTV Calculator

    Calculate customer acquisition cost, margin-adjusted lifetime value, your LTV:CAC ratio, and how many months it takes to pay back acquisition spend.

  • Discount Calculator

    Work out the final price after a discount (including stacked discounts), how much you save, or what percent off a sale price actually is.

  • Unit Economics Simulator

    Model your store's full unit economics: contribution margin per order, monthly P&L, break-even orders, and what a 0.5% fee change is really worth — shareable by URL.

Developer references & validators (6)

  • Stripe Test Cards

    Every Stripe test card number, searchable and one click to copy — successful payments, declines by code, fraud and Radar triggers, disputes, 3D Secure, international cards, and pm_ tokens.

  • Card Decline Code Lookup

    Look up any card decline code — Stripe codes, numeric issuer responses (05, 51…), AVS results, and Visa/Mastercard chargeback reasons — with who declined it, whether it is retryable, and what to do next.

  • MCC Code Lookup

    Search the full list of merchant category codes (MCCs) by number or description — the ISO 18245 codes card networks use to classify businesses for interchange, rewards, and risk.

  • IBAN Checker

    Validate any IBAN in your browser: country code, country-specific length, format, and the mod-97 checksum banks use. Nothing you type ever leaves the page.

  • Luhn Algorithm Checker

    Check whether any number passes the Luhn checksum, with a step-by-step visualization of exactly how the algorithm works — the check behind every card number.

  • UPC/EAN Check Digit Calculator

    Calculate or verify the check digit for any UPC-A, EAN-13, EAN-8, or GTIN-14 barcode number, with the GS1 mod-10 math shown step by step.

Store operations & templates (9)

  • SKU Generator

    Generate clean, consistent SKUs from a prefix, product attributes, and a numeric sequence — preview every combination and export as CSV. Runs entirely in your browser.

  • Chargeback Response Generator

    Pick the chargeback reason code and get a tailored evidence checklist plus a ready-to-edit rebuttal letter — for Visa and Mastercard disputes.

  • Invoice Generator

    Create a professional invoice in your browser and print or save it as a PDF — line items, tax, discounts, your logo. No account, no watermark, and your data never leaves the page.

  • Shipping Policy Generator

    Answer a few questions about your processing times, carriers, and international coverage — get a clear shipping policy you can paste into your store. No signup.

  • Inventory Turnover Calculator

    Calculate your inventory turnover ratio and days of inventory on hand from COGS and average inventory, with benchmarks for what a healthy ratio looks like.

  • EOQ Calculator

    Find the order quantity that minimizes total inventory cost — economic order quantity, orders per year, and an interactive curve of ordering vs holding costs.

  • Safety Stock Calculator

    Calculate safety stock from your demand variability, lead time, and target service level — including the combined formula for variable lead times.

  • Reorder Point Calculator

    Work out exactly when to reorder: average daily demand × lead time + safety stock, with the math shown and edge cases explained.

  • Sell-Through Rate Calculator

    Calculate sell-through rate from units sold and units received, with benchmarks by category and what to do when the rate is too low or too high.

Image & file tools (10)

  • HEIC to JPG Converter

    Convert iPhone HEIC photos to JPG right in your browser — bulk files, adjustable quality, and nothing ever uploaded to a server.

  • WebP to JPG Converter

    Convert WebP images to JPG instantly on your device — drag in multiple files, set quality, download. No upload, no signup, no watermark.

  • WebP to PNG Converter

    Convert WebP images to lossless PNG instantly in your browser — transparency preserved, multiple files at once, nothing uploaded anywhere.

  • AVIF to JPG Converter

    Convert AVIF images to JPG in one step, entirely in your browser — bulk conversion with adjustable quality and zero uploads.

  • PNG to JPG Converter

    Convert PNG images to smaller JPGs on your device — transparency flattened to white, quality slider, bulk files, no upload.

  • JPG to PNG Converter

    Convert JPG images to lossless PNG instantly in your browser — multiple files at once, nothing sent to any server.

  • PNG to WebP Converter

    Convert PNGs to modern WebP for dramatically smaller web images — adjustable quality, bulk files, all on your device.

  • JPG to WebP Converter

    Convert JPGs to WebP for faster pages and smaller files — quality slider, bulk conversion, zero uploads.

  • JPEG Compressor

    Compress JPEG photos to a fraction of their size with a quality slider and instant before/after readouts — all on your device, never uploaded.

  • PNG Compressor

    Shrink PNG files with 256-color quantization (the pngquant technique) right in your browser — typically 50–70% smaller with transparency preserved.