This isn't an article about 'flat vs lump-sum'. You answer 6 questions about your business and the tool computes all three forms at once, showing which leaves you with the most — and by exactly how much. You'll also see at what revenue the ranking flips, which is usually the key fact when choosing for a whole year.

Your situation — 6 questions

1. Monthly revenue (PLN)

2. Monthly costs (PLN)

3. ZUS stage

4. Lump-sum rate for your activity

Most common: 12% (IT, programming), 14% (medical, engineering), 15% (consulting, marketing), 8.5% (general services), 5.5% (construction), 3% (trade).

5. Filing jointly with a spouse?

6. Do you have children (child relief)?

Joint filing and child relief work only on the tax scale — this often decides the choice.

2026 model: social contributions by stage (preferential PLN 456.18 with sickness, full ZUS PLN 1,926.76), health: scale 9% of income (min PLN 432.54), flat 4.9% (min PLN 432.54, deduction cap PLN 1,175/month), lump-sum by annual thresholds (498.35 / 830.58 / 1,495.04). Scale: 12% up to PLN 120,000 annual base, 32% above, tax-free amount PLN 30,000, PIT-2 PLN 300/month. Joint filing computed with a simplified method (doubling the threshold and tax-free amount on a single income).

An indicative, informational estimate — not tax or legal advice. The choice of tax form has consequences for the whole tax year; consult an accountant or tax adviser before deciding.

Before you decide — traps the calculator can't price

Lump-sum: costs don't reduce the base. With high costs (equipment, goods, subcontractors) lump-sum usually loses despite a low rate.
Lump-sum: no joint filing with a spouse and no child relief. On a single-income household that can be thousands a year.
Flat tax: no tax-free amount and no joint filing, but health at 4.9% with a deduction cap. Usually pays off above roughly PLN 15,000 monthly income.
The lump-sum rate depends on your PKD code and the work actually performed — not on what the contract says. A wrong rate means tax arrears with interest.
You choose the form by the 20th day of the month following your first revenue of the year. Changing mid-year is generally not possible.
B2B for a former employer: flat tax and lump-sum are blocked if you perform the same duties as on your employment contract in the same year.