Common questions about CardLab and credit cards
CardLab is a private credit card tracker and simulator. These are short, self-contained answers about the product and about statement dates, grace periods, APR, utilization, and payoff. Educational only - not financial advice.
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About CardLab
What is CardLab?
CardLab is a private credit card tracker and simulator for iPhone and the web. You enter your own limit, APR, and dates, then practice purchases, payments, interest, and payoff. There is no bank login and no real card number. It is educational software, not a lender, a credit-score product, or the Danish biometric company CardLab ApS.
Does CardLab connect to my bank?
No. CardLab is a manual tracker and simulator - there's no bank login, no real card number, and no CVV. You enter your own cards and activity, so there's nothing to sync with a bank and nothing to break. By default everything you enter stays on your device; optional iCloud sync and the Cloud AI tutor are yours to turn on.
Will this change my real credit score?
No. CardLab is educational only. It shows an educational “Credit Health Meter,” not a credit score, and it does not predict scores, approvals, or lender decisions.
What does Pro unlock?
Unlimited cards, all country presets, the installment / cash advance / balance transfer labs, rewards and annual-fee breakeven, and every lesson. It is a one-time $9.99, with no subscription.
Is CardLab free?
Yes. The web simulator and the iPhone app are free to start: one simulated card, the timeline, payoff and utilization labs, five lessons, and the on-device tutor. CardLab Pro is a one-time $9.99 unlock. There is no subscription unless you choose the optional Cloud AI tutor.
How is CardLab different from a bank-connected tracker?
CardLab never logs into a bank and never asks for a real card number. You enter your own limit, APR, and dates, then practice on a timeline. Bank-connected apps pull live transactions from your accounts. CardLab is a sandbox for learning the billing cycle, not a replacement for your issuer app.
Does CardLab give financial advice?
No. CardLab is educational only. It models interest, grace, utilization, and payoff from numbers you enter. It does not calculate or predict real credit scores, approvals, or lender decisions, and it is not a substitute for your card's terms.
Billing cycle
What is a credit card statement date?
The statement date is the day your issuer totals the cycle into a statement balance. Purchases and payments posted up to that day are on this bill; anything after it lands on the next one. Most issuers also report that balance to the credit bureaus. CardLab walks through cutoff, due date, and grace together in the guide.
Should I pay before the statement date or the due date?
Pay before the statement date to lower the balance that is billed and reported as utilization. Pay the statement balance in full by the due date to avoid interest and keep the grace period. They do different jobs. Paying only by the due date still avoids interest; it does not change the number already reported.
How do credit cards calculate interest?
Your APR is divided into a daily periodic rate - APR divided by 365, or 360 at some issuers. That rate applies to each day's balance and the daily charges are added up. This is the average daily balance method. Pay each statement in full by the due date and the grace period keeps new purchases at zero interest.
The two key dates
What is a credit card statement date?
The statement date, also called the closing or cutoff date, is the day your issuer totals the cycle and freezes it into a statement balance. Purchases and payments posted up to that day are on this bill; anything after it lands on the next one. It is also when most issuers report your balance to the credit bureaus.
Is the statement date the same as the due date?
No. The statement date is when the bill is calculated; the due date is when it has to be paid, typically about three weeks later. The gap between them is your grace period. Confusing the two is the most common reason people are surprised by interest.
Should I pay before the statement date?
Paying before the statement date lowers the balance that gets billed and, more importantly, the utilization figure reported to the bureaus. Paying after it, by the due date, still avoids interest. So pay before the cutoff to report a lower number, and before the due date to stay interest-free.
What happens if I only pay the minimum by the due date?
Your account stays current and you avoid a late fee, but you lose your grace period. The unpaid statement balance starts accruing interest, and new purchases usually begin accruing from the day they post instead of being interest-free. Paying the minimum protects your record, not your wallet.
Should I pay the statement balance or the current balance?
Pay the statement balance in full by the due date. That is the amount the grace period is measured against, so paying it is what keeps new purchases interest-free. Paying the higher current balance is fine and lowers reported utilization, but it is not required to avoid interest.
What happens if I miss a credit card due date?
You typically owe a late fee and lose your grace period, so interest starts accruing. A payment 30 or more days late can also be reported to the credit bureaus, which is far more damaging than the fee. If you are only a few days late, pay immediately and ask for the fee to be waived.
What is a grace period on a credit card?
The grace period is the stretch between your statement date and your due date - usually 21 to 25 days - during which new purchases do not accrue interest. You only get it if you paid your previous statement balance in full and on time. It is a reward for paying in full, not an automatic feature.
How do I get my grace period back after losing it?
Pay your full statement balance by the due date, then do it again the following cycle. Most issuers restore the grace period after two consecutive paid-in-full statements. Until it is back, every new purchase accrues interest from the day it posts, so there is no interest-free window to plan around.
Do cash advances and balance transfers have a grace period?
Almost never. Cash advances start accruing interest the day you take them, at a higher APR, plus an upfront fee. Balance transfers vary but usually have no grace period on new purchases unless the card is paid in full. Only ordinary purchases are normally covered.
What you owe
What is the difference between statement balance and current balance?
The statement balance is the amount frozen on your closing date - what the bill actually asks for. The current balance is everything you owe right now, including purchases made after the statement closed. The current balance is usually higher, and the difference is simply this cycle so far.
Which balance do I pay to avoid interest?
Pay the statement balance in full by the due date. That is the number your grace period is measured against, so clearing it keeps new purchases interest-free. Paying the current balance does no harm and lowers reported utilization, but it is not what avoids interest.
Why is my current balance higher than my statement balance?
Because you have spent since the statement closed. Those purchases belong to the next cycle and are not due yet. If the current balance is lower instead, a payment or refund posted after the statement closed - you may still owe the statement amount to keep the grace period.
How is a credit card minimum payment calculated?
Most issuers charge the greater of a flat floor - often around $25 to $35 - or a small percentage of your balance, commonly 1% to 3%, plus that cycle's interest and fees. Because the percentage shrinks as the balance falls, the payoff gets slower the longer you carry a balance.
What is the minimum payment trap?
Paying only the minimum covers the interest and fees first, so very little goes to principal. A balance carried at a typical APR can take well over a decade to clear and cost more in interest than the original purchases. The payment feels affordable precisely because it barely reduces the debt.
How much more than the minimum should I pay?
Any fixed amount above the minimum helps, because it stays flat while the minimum shrinks. Paying a steady amount rather than a percentage typically cuts a multi-year payoff to months. CardLab lets you compare minimum-only against a fixed payment on your own balance and APR.
How do you calculate credit utilization?
Divide your balance by your credit limit and multiply by 100. A $1,450 balance on a $3,000 limit is roughly 48% utilization. It is measured per card and across all your cards combined, normally using the balance reported on each statement date.
What is a good credit utilization ratio?
Lower is generally treated as healthier, and staying under about 30% is the common rule of thumb. Utilization is recalculated every time a new balance is reported, so a high month is not permanent - it is a snapshot, not a record.
How can I lower my reported utilization?
Pay down the balance before the statement date rather than the due date, since the statement balance is what gets reported. Requesting a higher limit or spreading spending across cards also lowers the ratio. Paying in full after the statement closes avoids interest but does not change the number already reported.
What it costs
How is credit card interest actually calculated?
Your APR is divided into a daily periodic rate - APR divided by 365, or 360 at some issuers. That rate is applied to each day's balance across the cycle and the daily charges are added up. This is the average daily balance method, which is why paying earlier in the cycle costs less than paying on the due date.
What APR will I actually pay if I never carry a balance?
Effectively zero on purchases. As long as you pay each statement balance in full by its due date, the grace period keeps new purchases interest-free and the APR never applies. The rate only starts mattering the first month you carry a balance forward.
Is a lower APR always better?
It matters only if you carry a balance. If you pay in full every cycle, the APR is irrelevant and rewards or fees decide which card is better. If you do carry a balance, APR is the single largest cost and outweighs almost any rewards rate.
Why are credit card cash advances so expensive?
Three costs stack at once: an upfront fee, typically around 3% to 5% of the amount with a minimum charge; a cash advance APR that is usually higher than the purchase APR; and no grace period, so interest accrues from day one. A small advance can cost far more than its size suggests.
Does a cash advance hurt my credit score?
Not directly - credit reports do not flag a balance as a cash advance. The indirect effect is real, though: the advance plus its fee raises your balance and therefore your reported utilization, and the fast-accruing interest makes the balance harder to clear.
What counts as a cash advance?
ATM withdrawals on a credit card are the obvious case, but issuers also treat convenience checks, wire transfers, money orders, casino chips, and often peer-to-peer or crypto purchases the same way. Check the terms before treating a card like cash - the classification is the issuer's, not yours.
Are credit card rewards worth it if I carry a balance?
Almost never. Earning 1.5% cashback while paying a 24% APR means the interest costs roughly sixteen times what the rewards return. Rewards are calculated once on what you spend; interest compounds on what you owe. Clearing the balance beats optimizing the rewards rate every time.
When is an annual fee card worth paying for?
When the rewards and benefits you will actually use exceed the fee, and you pay in full each cycle. Divide the fee by your rewards rate to find the spend you need to break even - a $95 fee at 2% back needs about $4,750 of annual spend before it pays for itself.
How much interest cancels out my cashback?
A single month of carried balance usually erases a year of rewards on that spend. At 1.5% back and a 24% APR, roughly one month of interest costs more than the cashback earned on the same amount. CardLab shows the exact crossover point using your own APR and balance.
Calculators
How long will it take to pay off $5,000 in credit card debt?
At 24.99% APR, paying $200.00 a month clears $5,000.00 in 3 years and costs $2,135.18 in interest. Paying only the minimum on the same balance never clears it, because the minimum barely covers the interest charged each month.
Does paying twice a month pay off a credit card faster?
Slightly, and for a specific reason: interest is calculated on each day's balance, so money that arrives earlier in the cycle reduces more daily balances. The effect is real but small - the amount you pay matters far more than the timing of it.
Is it better to pay off the highest APR or the smallest balance first?
Highest APR first - the avalanche method - always costs less in total interest. Smallest balance first, the snowball, costs more but clears individual cards sooner, which some people find easier to sustain. The gap is usually modest, and a plan you actually finish beats an optimal one you abandon.
How much interest will I pay on a $5,000 credit card balance?
At 24.99% APR, $5,000.00 costs about $3.42 a day, or roughly $102.70 over a 30-day cycle. That is the cost of carrying it for one month; the total depends on how fast you pay it down.
Why was I charged interest when I paid my balance?
Usually residual interest. If you carried a balance last cycle, interest kept accruing between the statement date and the day your payment landed, so a charge appears on the next statement even though you paid in full. Paying in full again clears it and restores the grace period.
Does a 0% APR card really charge no interest?
On the balances the promotion covers, yes, until it expires. Purchases may be excluded if the offer is for balance transfers only, and cash advances are almost never included. Deferred-interest offers are different again: miss the deadline and the whole accrued amount is charged retroactively.
How is the minimum payment on a credit card calculated?
Most US issuers charge the greater of a flat floor, commonly $25 to $35, or 1% to 3% of the balance, plus the cycle's interest and fees. On $5,000.00 at 24.99% APR with a 2% or $35 rule, the first minimum is about $100.00.
What happens if I only ever pay the minimum?
You stay current and avoid late fees, but you lose the grace period and most of each payment goes to interest. On $5,000.00 at 24.99% APR the balance never clears at all - the minimum barely covers the interest charged each month.
Does paying the minimum hurt your credit score?
Paying the minimum on time keeps your payment history clean, which is the largest scoring factor. The indirect damage is utilization: a balance that barely moves stays reported month after month, and high utilization is the second largest factor in most scoring models.