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Interest rate differential calculator

Holding a currency pair overnight earns or pays the gap between two interest rates. See that gap, and what it means for your position per day, over your hold and over a year.

Position on AUD/USD
Over the holding time–
Rate gap for your side–
After the markup–
Per day–
Per year–
Position value–

Rates come from the central bank table (checked 5 Nov 2026); type your own to try another case.

Runs in your browser; nothing you type is sent anywhere. For learning and planning only, not financial advice. Check your broker's contract specification before trading.

How carry works

Buying EUR/USD means holding euros and owing dollars. You earn the euro rate on one side and pay the dollar rate on the other, so the position collects the difference. If the currency you buy has the higher rate, the carry is in your favour; if it has the lower rate, you pay it every night. The calculator works it out on the position's value: value × (rate of the bought currency − rate of the sold one − broker markup) ÷ 365 per day.

An example: a 1-lot AUD/USD buy at 0.6600 is worth $66,000. With the RBA at 4.60 % and the Fed at 4.00 %, the gap is 0.60 % a year; less a 0.50 % markup it leaves 0.10 %, about $0.18 a day. Sell the same lot and you pay the gap plus the markup: about $2.00 a day.

Why your broker's swap differs

Brokers do not pay the policy rates themselves. They use interbank rates for the period, add their own markup on both sides, and charge three days of swap on one weekday (usually Wednesday) to cover the weekend. So treat this as the reason behind the swap and a check on whether your broker's numbers are fair, not as the exact amount you will see.

The rates are filled in from the central bank interest rates table; you can type your own. Size the trade with the lot size calculator.

Questions

What is an interest rate differential?

The gap between the interest rates of two currencies. In forex it decides whether a position held overnight earns or pays swap.

Why do I pay swap on both buy and sell?

Brokers add a markup on each side. When the rate gap is small, the markup is larger than the gap, so both directions pay.

Why is swap tripled on Wednesday?

A trade open on Wednesday night settles over the weekend, so most brokers charge three days at once; check your broker's day.

Which rate does the calculator use for the dollar?

The top of the Fed's target range, from the central bank table. Type another rate if you prefer.

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