Apr Per Month Calculator
An APR is quoted for a year, but interest is charged month by month. This APR per month calculator converts any annual percentage rate into the two monthly rates that matter: the nominal monthly rate (APR divided by 12, the rate your card or loan actually applies each billing cycle) and the effective monthly rate (the rate that, compounded for 12 months, lands exactly on the stated APR). Add a balance and it also shows what one month of interest costs under each method.
The two answers are close but never equal, and mixing them up is the most common APR mistake. At 18% APR the nominal rate is 1.5000% a month and the effective rate is 1.3888% a month. On a $5,000 balance that gap is worth $5.56 in a single month: $75.00 of interest at the nominal rate against $69.44 at the effective rate.
The nominal rate is the one used for billing on credit cards and in the payment formula of amortizing loans. The effective rate is a comparison tool: it strips compounding out so different offers can be judged on the same footing.
Quick Answer
Key takeaways
- Nominal monthly rate = APR divided by 12. This is the periodic rate credit cards bill and loan amortization uses.
- Effective monthly rate = (1 + APR) to the power 1/12, minus 1. It is always a little lower, because compounding does part of the work.
- One month of interest = balance times the monthly rate. At 18% APR on $5,000 that is $75.00 billed, or $69.44 on a true compounded basis.
- Cards actually compound daily in most cases, so a carried balance costs slightly more over a year than the monthly view suggests.
- Quick Answer
- Nominal vs effective: two rates, two different questions
- The two formulas, and when each one applies
- Worked example: 18% APR on a $5,000 balance
- Quick reference: what common APRs cost per month
- Which rate shows up on cards, loans and savings accounts
- APR, APY and the note rate are three different numbers
- What competing calculators miss
- Frequently asked questions
- Add This Calculator to Your Website
Nominal vs effective: two rates, two different questions
The nominal rate answers “what will I be charged this month?” and the effective rate answers “what is this APR really costing me once compounding is stripped out?” Most conversion tools give you only the first answer, APR divided by 12, and stop. That is fine for predicting a credit card bill, because the nominal periodic rate is genuinely how issuers bill: the Consumer Financial Protection Bureau describes APR in its credit card key terms as the standard yearly cost figure, and issuers apply it in monthly (and usually daily) slices.
The effective rate exists because division hides compounding. Roll the nominal 1.5% a month forward for twelve months and you do not get 18%: you get (1.015)^12 minus 1, which is about 19.56%. So the monthly rate that compounds to exactly 18% has to be smaller, and it is: 1.3888%. Neither number is a trick. They are two conventions, and the skill is knowing which question you are asking.
The two formulas, and when each one applies
Both formulas start from the same APR. They diverge on one point: whether interest earned or charged in one month itself starts accruing interest in the next.
Use the nominal rate when
- Predicting a credit card finance charge for the month.
- Checking a loan amortization schedule, where the payment formula uses APR divided by 12.
- An offer quotes a “monthly rate” that was clearly produced by dividing an APR by 12.
Use the effective rate when
- Comparing two offers with different compounding or quoting conventions.
- Converting an APR into an equivalent monthly growth rate for savings or investment math.
- You want the annual figure and the monthly figure to agree exactly over a full year.
Worked example: 18% APR on a $5,000 balance
The calculator above is pre-filled with this case, and every number below is what it returns when you press Calculate.
| Figure | Value |
|---|---|
| APR entered | 18% |
| Nominal monthly rate (18 ÷ 12) | 1.5000% |
| Effective monthly rate ((1.18)^(1/12) − 1) | 1.3888% |
| One month of interest on $5,000, nominal | $75.00 |
| One month of interest on $5,000, effective | $69.44 |
| Gap in one month | $5.56 |
Read the gap the right way round. Your card will bill you on the nominal basis, so $75.00 is the realistic first-month figure on a steady $5,000 balance. The $69.44 tells you what the same APR means as pure compounded growth, which is the fair basis for comparing it against, say, a savings yield quoted as an effective rate. If you want the annual picture behind the monthly one, the cost of interest calculator totals what a rate costs over the full term of a debt.
Quick reference: what common APRs cost per month
These are the same five rates the calculator uses for its reference table, computed with the two formulas above. The pattern to notice is that the compounding gap widens as the APR climbs: at 12% it is about 0.05 points a month, at 30% it is nearly 0.29 points.
| APR | Nominal per month | Effective per month | Gap |
|---|---|---|---|
| 12% | 1.0000% | 0.9489% | 0.0511 points |
| 15% | 1.2500% | 1.1715% | 0.0785 points |
| 18% | 1.5000% | 1.3888% | 0.1112 points |
| 24% | 2.0000% | 1.8088% | 0.1912 points |
| 30% | 2.5000% | 2.2104% | 0.2896 points |
Card APRs in the mid-20s are now ordinary: the Federal Reserve’s G.19 release tracks the average rate on interest-bearing card accounts, and it has sat above 20% in recent years. If you are comparing several cards at once, the average interest calculator helps you sanity-check a rate against the rates on your other debts before you convert it.
Which rate shows up on cards, loans and savings accounts
Credit cards bill on a daily periodic rate (APR divided by 365) applied to your average daily balance, which is the nominal convention sliced thinner; the monthly figure from this calculator is the close monthly equivalent. Amortizing loans such as mortgages and auto loans use APR divided by 12 inside the standard payment formula, again the nominal convention. Savings products are the mirror image: they quote APY, an effective annual yield, precisely because regulators wanted the compounding included rather than hidden.
One wrinkle matters for loans: a mortgage APR bundles some fees into the annual figure, so dividing it by 12 gives you the periodic rate of the APR, which is slightly higher than the periodic rate of the note rate used to compute the actual payment. For the full annual cost of a loan including fees, the annual effective borrowing cost calculator works the problem from the other direction. Regulation Z under the Truth in Lending Act is what forces lenders to disclose APR in this standardized way in the first place.
APR, APY and the note rate are three different numbers
APR is a nominal annual cost: periodic rate times periods, with loan fees folded in for installment credit. APY is an effective annual yield: it includes compounding, so for the same underlying rate APY is always equal to or higher than APR. The note rate is the raw interest rate on a loan contract before fees, which is why a mortgage can show a 6.5% note rate and a 6.7% APR on the same paperwork.
This page is strictly about the monthly conversion of an APR. If your starting point is a yearly interest amount rather than a percentage rate, the annual interest to monthly calculator splits an annual interest figure into monthly amounts instead. Keeping the two apart matters: a rate converts with division or a twelfth root, while a dollar amount converts with division alone.
What competing calculators miss
We checked the tools and guides ranking for this keyword before rebuilding the page. The pattern is consistent: nearly all of them divide by 12 and stop.
Winning move 1: both conventions, every time. CalculatorsHub, Brave Calculator and the top-ranking guides give a single monthly number produced by division. None of them shows the effective rate, so a reader comparing a card APR against an effective yield is comparing two different conventions without knowing it. This calculator returns both, labeled by the question each one answers.
Winning move 2: dollars on a real balance. A percentage alone does not change behavior; $75.00 a month does. The optional balance turns the conversion into a cost, under both conventions, which the simple converters never attempt. The one competitor with deeper math, GraphCalc’s periodic rate tool, handles any compounding frequency but buries the answer in academic notation and never prices a balance.
Winning move 3: numbers that match the tool. The previous version of this page printed the effective rate as 1.3889% while its own calculator computed 1.3888%. Small, but a conversion page lives or dies on exact figures. Every number in this article was re-run against the calculator code, and the Quick Answer, worked example and reference table all agree with what the tool displays.
Frequently asked questions
Divide by 12 for the nominal monthly rate: an 18% APR becomes 1.5000% per month. That is the rate credit cards and most loans actually apply each billing cycle. For the compounding-adjusted effective rate, use (1 + APR) to the power 1/12 minus 1, which gives 1.3888% at 18% APR.
The nominal rate is the APR spread evenly across 12 months. The effective rate is the monthly rate that compounds to exactly the stated APR over a year, so it is always slightly lower. At 24% APR the two are 2.0000% and 1.8088% per month.
Because compounding multiplies. Rolling the nominal monthly rate forward for twelve months produces more than the stated APR: 1.5% a month compounds to about 19.56% over a year. The effective rate that lands exactly on 18% therefore has to be a bit smaller, at 1.3888%.
The nominal convention. Issuers divide the APR into a daily periodic rate (APR divided by 365) and apply it to your average daily balance. The monthly nominal rate from this calculator is the monthly equivalent of that billing method. The effective rate is for comparisons, not billing.
About $75.00 in the first month on a steady balance, using the nominal rate your card bills. On a pure compounded (effective) basis the same month is $69.44. In practice the balance changes as you spend and pay, and daily compounding nudges the real figure slightly above the simple monthly estimate.
No. APR is a nominal annual rate that excludes compounding. APY, annual percentage yield, includes compounding, so APY is always equal to or higher than APR for the same underlying rate. Savings accounts quote APY; credit products quote APR.
Almost. The payment formula uses the note rate divided by 12. A mortgage APR also folds in some fees, so APR divided by 12 is slightly higher than the rate behind the actual payment. For credit cards and most other loans, APR divided by 12 is the periodic rate used.
Yes. Multiply a nominal monthly rate by 12 to get the nominal APR: 1.5% a month becomes 18% APR. If the monthly rate is an effective rate, the matching effective annual rate is (1 + monthly rate) to the power 12, minus 1: 1.3888% a month becomes exactly 18% over a year.
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References
- Consumer Financial Protection Bureau, “Credit cards key terms” – defines APR as the standard yearly cost of borrowing and explains how issuers must disclose it. CFPB: Credit Cards Key Terms. Accessed October 2026.
- Board of Governors of the Federal Reserve System, “Consumer Credit (G.19)” – the monthly statistical release tracking average APRs on interest-bearing credit card accounts. Federal Reserve: G.19 Consumer Credit Release. Accessed October 2026.
- Consumer Financial Protection Bureau, “Regulation Z, 12 CFR Part 1026” – the Truth in Lending rules that standardize how APR is calculated and disclosed. eCFR: Regulation Z (Truth in Lending). Accessed October 2026.
- Investopedia, “Annual Percentage Rate (APR): What It Means and How It Works” – APR definition, calculation and how it differs from the interest rate on a loan. Investopedia: Annual Percentage Rate (APR). Accessed October 2026.
- Investopedia, “Annual Percentage Yield (APY)” – how APY includes compounding, and why it is equal to or higher than APR for the same underlying rate. Investopedia: Annual Percentage Yield (APY). Accessed October 2026.
- Investopedia, “Effective Annual Interest Rate” – the effective rate formula and how compounding frequency changes the true annual cost. Investopedia: Effective Annual Interest Rate. Accessed October 2026.
- Investopedia, “Periodic Interest Rate” – the periodic rate concept behind APR divided by 12 and APR divided by 365. Investopedia: Periodic Interest Rate. Accessed October 2026.
- Investopedia, “Nominal Interest Rate” – the nominal rate definition used for the APR divided by 12 convention. Investopedia: Nominal Interest Rate. Accessed October 2026.
- Investopedia, “Compound Interest” – how interest on interest accumulates, the mechanism behind the nominal versus effective gap. Investopedia: Compound Interest. Accessed October 2026.
- US Securities and Exchange Commission, Investor.gov, “Understanding Fees” – how rates and fees compound against a balance over time. Investor.gov: Understanding Fees. Accessed October 2026.