Methodology
This page explains the math behind every calculator on CalcMyCard, in full detail, so you can verify our results or understand exactly where a number came from.
Interest calculation method
Our calculators model interest using a monthly rate equal to your card’s APR divided by 12, applied to the balance remaining at the start of each month, iterated forward month by month until the balance reaches zero. This is the same simplified approach used by most public credit card calculators, and it typically falls within a few dollars of an issuer’s true daily-average-balance calculation over a full payoff timeline. Our dedicated Daily Periodic Rate Calculator exposes the true APR ÷ 365 daily rate for anyone who wants that specific, more granular figure.
Minimum payment formulas
Our Minimum Payment Calculator supports two common issuer formulas: a flat percentage of balance, and interest-plus-one-percent-of-principal (whichever is greater), both subject to a configurable dollar floor. These mirror the two most common minimum payment structures disclosed in major card issuers’ cardholder agreements.
Snowball and avalanche simulation
Our Multi-Card Debt Payoff Calculator simulates every card accruing interest monthly, minimum payments applied to every open card, and a shared extra payment amount funneled entirely to the current target card (smallest balance for snowball, highest APR for avalanche), rolling to the next target once a card reaches zero.
Balance transfer and consolidation comparisons
Our transfer and consolidation calculators model a one-time fee added to principal, a blended interest rate schedule (promotional rate during the promo window, standard rate after), and a fixed installment-loan payment formula for consolidation loans, to produce an apples-to-apples total cost comparison.
What our calculators don’t account for
Our tools don’t model card-specific quirks like exact grace period rules, promotional deferred-interest structures, or fees beyond what you explicitly enter. They’re built for clear, general-purpose estimation — always confirm exact figures against your official statement or cardholder agreement before making a financial decision.
Privacy of your inputs
Every calculation runs entirely in your browser using JavaScript. The numbers you enter are never transmitted to our servers, stored, or shared with any third party.