Why does an unused credit card lower your borrowing capacity?

The bank looks not at how much you have spent on the card, but at how much you COULD spend in a single day. It treats the granted limit as a liability and usually adds around 3% of the limit a month to your commitments. A card with a PLN 20,000 limit means PLN 600 of monthly commitments to the bank - even if the balance is zero. In our model this lowers borrowing capacity by about PLN 66,000.

What is the 2.5-point buffer from Recommendation S?

The KNF requires banks to assess borrowing capacity at an interest rate raised by a buffer of at least 2.5 percentage points. This way the bank checks whether you can cope with the payment if interest rates go up. For a loan at 7.5%, borrowing capacity is calculated as if the loan cost 10%. In our example the buffer lowers borrowing capacity from PLN 608,938 to PLN 495,213 - that is, by PLN 113,725.

How can you improve your borrowing capacity quickly?

The fastest fix is closing credit cards and overdraft limits - just cutting a card limit from PLN 20,000 to zero recovers about PLN 66,000 of borrowing capacity in our model and costs nothing. After that: paying off small instalment loans and purchases on instalments, adding a co-borrower with a stable income, a bigger down payment and extending the loan term - although at high rates the last one gives little and costs a great deal of interest.

Borrowing capacity

How a bank really calculates your borrowing capacity

Q: What is the DSTI ratio?

DSTI (Debt Service to Income) is the share of all your loan payments in your monthly net income. If you earn PLN 9,000 net and your payments total PLN 3,600, your DSTI is 40%. Following Recommendation S of the KNF (Polish Financial Supervision Authority), banks usually do not go above 40-50% - the lower the income, the more cautious the limit, because after paying the instalments there has to be a realistic amount left to live on.

The bank does not ask "how much do you earn?". The bank asks "how much will you have left when rates rise by 2.5 points and you still need to eat?". That is a completely different question - and it is why the calculated borrowing capacity usually disappoints.

9 min read · 14 July 2026 · Piotr Litwa, KredytPartner

The model in one sentence

The bank calculates your borrowing capacity in two moves. First it works out the maximum monthly payment you can handle. Then it checks what loan that payment could repay - but at an interest rate raised by a safety buffer.

max. payment = min( income - living costs - instalments - cards ; DSTI · income - instalments - cards )

The bank takes the lower of two numbers:
1) how much is actually left in your pocket after paying for living costs and commitments,
2) how much the DSTI limit allows - i.e. the maximum share of instalments in your income.

With the maximum payment in hand, the bank reverses the annuity payment formula:

capacity = payment · [ 1 - (1 + i)^-n ] / i

payment - the maximum payment from the previous formula
i - the monthly rate, but with the buffer: (interest rate + 2.5 percentage points) / 12
n - the number of instalments (25 years = 300)

The whole game is about that "with the buffer". It is one line that can wipe PLN 100,000 off your borrowing capacity.

DSTI: the first barrier

DSTI (Debt Service to Income) is the share of all instalments in your net income. If you take home PLN 9,000 and your instalments add up to PLN 4,500, your DSTI is 50%.

Recommendation S of the KNF (Polish Financial Supervision Authority) does not set one rigid threshold, but tells banks to apply a limit that is more cautious the lower the income. In practice banks work in a range of 40-50%, and for income close to the minimum wage they can go lower. The logic is simple: 50% of PLN 20,000 leaves PLN 10,000 to live on, while 50% of PLN 4,000 leaves PLN 2,000 - and you cannot support a family on the latter.

Work out your DSTI in 5 seconds

Add up all your instalments (loans, leasing, purchases on instalments, maintenance payments) and divide by your net income. Above 50% - you are unlikely to get a loan. Below 35% - you are in the comfort zone.

The 2.5-point buffer: the bank tests you for bad times

This is the most important thing in this article. The bank does not calculate your borrowing capacity at the interest rate it is offering you. In Recommendation S, the KNF requires the assessment to be carried out at a rate raised by a buffer - of at least 2.5 percentage points.

The reason is sensible and follows directly from what happened in Poland in 2021-2022, when rates rose several times over a dozen or so months and mortgage payments almost doubled. So the bank asks: could you cope with the payment if rates go up? If the answer is "no", you do not get the loan. Even if today you can afford it with room to spare.

Let's take a concrete case. A two-person household, net income PLN 9,000, living costs PLN 2,500, no other commitments, a mortgage over 25 years at 7.5%:

Method of calculation	Test rate	Max. payment	Borrowing capacity
If the bank did the maths "like a normal person" (7.5%)	7.5%	PLN 4,500	PLN 608,938
How it really calculates (7.5% + 2.5-point buffer)	10.0%	PLN 4,500	PLN 495,213

The buffer costs PLN 113,725 of borrowing capacity

The same person, the same income, the same payment - and a PLN 113,725 difference in the loan amount. Not because you did something wrong. Because the bank has to assume that rates will rise.

The paradox: the actual payment you will make at 7.5% will be PLN 3,659.58, not PLN 4,500. The bank leaves you a PLN 840 monthly margin - and that is exactly the buffer, turned into cash.

A credit card: a debt you never took on

You have a credit card with a PLN 20,000 limit. You have never used it. Balance: zero. To the bank this makes no difference at all.

The bank looks not at how much you have spent, but at how much you could spend tomorrow. It treats the granted limit as a liability and usually adds around 3% of the limit a month to your commitments (some banks 3%, some 5% - in our calculator we assume 3%). The same rule covers an overdraft limit on your current account.

Card limit	Burden according to the bank (3%)	Borrowing capacity	How much you lose
no card	PLN 0	PLN 495,213	-
PLN 5,000	PLN 150/month	PLN 478,705	-PLN 16,508
PLN 10,000	PLN 300/month	PLN 462,198	-PLN 33,015
PLN 20,000	PLN 600/month	PLN 429,184	-PLN 66,029
PLN 50,000	PLN 1,500/month	PLN 330,142	-PLN 165,071

The card you don't use costs PLN 66,000

A PLN 20,000 limit, a PLN 0 balance, zero interest, "it doesn't cost me anything, does it?". It costs PLN 66,029 of borrowing capacity - roughly what a room in a flat costs.

What to do: if you are planning a mortgage, close your cards and limits at least 2-3 months before applying - that is roughly how long it takes for the data in BIK (Poland's credit bureau) to be updated. Get a certificate of closure from the bank. This is the cheapest way to improve borrowing capacity there is: it costs one visit and zero zloty.

Living costs and the number of people in the household

The bank will not take your word for "I spend PLN 800 a month". It applies its own minimum, depending on the number of people in the household - and takes the higher of the two values: its own minimum or what you declared.

Each child means another few hundred zloty of fixed costs in the bank's model. There is nothing malicious about it: the bank has to assume that your expenses will not disappear when a loan payment appears.

Two earners instead of one

Income PLN 9,000, costs PLN 2,500 → borrowing capacity PLN 495,213.
Income PLN 15,000 (two people), costs PLN 3,300 → borrowing capacity PLN 825,354.

Living costs rise, but more slowly than income. That is why adding a co-borrower with a stable income is usually the most effective single move - provided you understand the consequences: you are jointly and severally liable for the loan, and if you split up, getting out of the agreement can be harder than getting out of a marriage.

What improves borrowing capacity

1. Closing cards and limits - immediately, for free

Covered above. The biggest return for the least effort: +PLN 66,029 for closing one card with a PLN 20,000 limit.

2. Paying off small instalment loans

A PLN 800 monthly instalment (e.g. for a phone and a TV bought on instalments) lowers borrowing capacity by PLN 88,038. Every zloty of monthly instalment costs you about PLN 110 of borrowing capacity. It is worth doing the maths before you buy anything "in twelve 0% instalments" - especially since "zero percent" usually does not mean zero cost.

3. Down payment

A down payment does not increase your borrowing capacity - it increases the price of the property you can afford. That is an important difference. With a borrowing capacity of PLN 495,213 and a down payment of PLN 150,000, you can buy a flat for PLN 645,213.

But the down payment has a second, less obvious effect: with a down payment below 20%, the bank usually adds low down payment insurance, which raises the margin, and so the interest rate - and a higher interest rate lowers borrowing capacity. A 20% down payment is not a bank's whim, it is a pricing threshold.

4. A longer loan term - with a big caveat

Extending the term lowers the payment, so it increases borrowing capacity. But at high rates the effect is surprisingly weak, and the price is very high:

Term	Borrowing capacity	Payment (on PLN 495,213, 7.5%)	Total interest
20 years	PLN 466,311	PLN 3,989.40	PLN 462,244
25 years	PLN 495,213	PLN 3,659.58	PLN 602,661
30 years	PLN 512,779	PLN 3,462.60	PLN 751,323

Extending from 25 to 30 years: +PLN 17,566 of borrowing capacity, +PLN 148,662 of interest

Five extra years give you PLN 17,566 more borrowing capacity and cost PLN 148,662 in extra interest. That is the worst exchange rate in this whole article: PLN 8.46 of interest for every zloty of borrowing capacity.

At high rates most of the payment goes on interest anyway, so stretching the loan hardly lowers the payment - it just makes you pay for longer. If you have to extend the term to get the loan, that is a sign the loan is simply too big.

5. A stable form of employment

A permanent employment contract is the gold standard for a bank. A fixed-term contract, a contract of mandate, a contract for specific work, B2B - each of them requires a longer history (usually 6-24 months) and may be averaged downwards. A sole-trader business with a short track record is the hardest case: the bank will calculate income from the last 12 months, often reduced by depreciation.

What destroys borrowing capacity

Four things that close the door to a loan

1. Payday loans in your BIK history. This is the worst entry you can have. Even a payday loan repaid on time is a signal to the bank: "when this person was in need, they reached for a loan with an APR of several hundred percent". The entry stays in BIK for years. Some banks reject the application automatically.

2. Many credit enquiries at once. Every application you submit is an enquiry visible in BIK. Five applications in a month reads like desperation - the bank assumes someone has already turned you down. Submit applications carefully and within a narrow time window, after comparing offers first, not blindly.

3. Late payments. Even a few days late. The BIK score reacts very sharply to any delay of more than 30 days, and the history follows you for years.

4. Unstable income. Changing jobs just before applying, a probation period, income that has fallen in recent months - the bank will average all of this to your disadvantage.

An empty BIK record is a problem too

Having no credit history at all is not an advantage. The bank has nothing to base its assessment on, so it treats you cautiously. A credit card with a small limit, used and paid off in full every month for a year, builds a positive history - and then, a few months before applying for a mortgage, you close it to win back borrowing capacity. Yes, it is a bit of gaming the system. But that is how the system works.

Summary: what to do, and when, before applying

6 months before: stop submitting any credit applications and buying anything on instalments.
3 months before: close your credit cards and overdraft limits. Get the certificates.
3 months before: pay off small instalment loans and purchases on instalments - every PLN 800 of instalment is PLN 88,038 of borrowing capacity.
1 month before: download your own BIK report and check it for errors. They do happen.
When applying: calculate your borrowing capacity in the calculator with the buffer, so you know what to expect.

Do the maths yourself

Calculator

Borrowing capacity calculator

A model following the logic described in this article: DSTI, the KNF buffer, the burden of card limits and living costs depending on the number of people. You will also see how much your borrowing capacity goes up when you close a card - using your own numbers.

Check your borrowing capacity

Loan repayment calculator

See how the payment and total interest change with different terms and interest rates.

Calculate the payment

Debt consolidation calculator

Several instalments rolled into one - a lower payment, but usually a higher cost. We show both effects.

Calculate consolidation

Read on

APR or interest rate? - before you calculate your borrowing capacity, learn to recognise what a loan really costs.
Overpay your loan or invest? - already have a loan and PLN 20,000 to spare? This text calculates both scenarios.
Compound interest from scratch - the mechanism that makes a 25-year loan at 7.5% cost more in interest than the loan itself.

All borrowing capacity amounts were calculated with our educational model (js/finance.js) on these assumptions: net income PLN 9,000, a 2-person household, living costs PLN 2,500, DSTI 50%, interest rate 7.5%, term 25 years, a 2.5-point buffer, a card limit burden of 3% a month. Every bank has its own scoring and its own parameters - the actual lending decision may differ from these calculations. This text is educational and does not constitute credit advice.