The fee comes first
A balance transfer commonly carries a fee, set as a percentage of the amount moved, and it is added to the new balance on day one. A 3% fee on $1,000 is $30, so the new card starts at $1,030.
Even with a 0% promo, that fee is a real cost. It is the price of the lower rate, and every comparison in the calculator includes it. Because the fee is a percentage, it grows with the amount moved.
The promo clock
The promo rate, often 0%, lasts until a set month. After that, whatever balance is left starts collecting interest at the post-promo APR. The calculator shows two key numbers here:
- What's left at promo end at your monthly payment.
- The payment that clears it inside the promo. At 0%, $1,030 over 12 months is about $86 a month.
If the promo rate is above 0%, a small amount of interest builds during the promo as well, and the payment needed to clear it in time rises a little to cover that. The end date matters as much as the rate. A payment that clears the balance one month after the promo ends puts that last month at the higher APR.
Side by side with staying put
On the current card, the cost is the interest at the current APR, month after month, at the same payment. On the transfer card, the cost is the fee plus any interest during the promo plus any interest after it ends.
Both paths use the same monthly payment, so the only things that differ are the rates, the fee and the timing. That keeps the comparison focused on cost alone rather than on how much goes out each month.
Which path costs less comes down to a few things:
- Fee size: a larger fee takes more of the interest savings.
- Promo length: a longer promo gives the payment more months at the low rate.
- Payment amount: when the payment clears the balance inside the promo, the fee is close to the whole cost.
- Post-promo APR: if a large balance remains and the new rate is higher than the old one, the gap can narrow or flip.
What the comparison leaves out
The calculator assumes the full balance moves at once, no new purchases on either card, and steady rates. New purchases on a transfer card can carry a different rate, and how payments are split between balances varies by card agreement. Promo terms also vary, so the card's own terms are the final word.
A “no interest if paid in full” offer is a different setup; the deferred interest calculator covers it. For replacing several debts with one fixed-rate loan, the debt consolidation calculator runs that comparison, and the credit card interest calculator breaks down the current card's interest by day and month.