What this tool does. It pulls the current Binance perpetual funding rate for the contract you select, then translates it into an annualized rate, a daily rate, a daily dollar cost, and the same cost restated against your margin. The pull happens on page load and on every contract switch; the status pill in the card header tells you whether the number on screen is live or the static fallback. Typing a rate in by hand overrides the fetched value and does not send a new request.
Three things the quoted rate is not telling you.
Funding looks small per interval and large over time. The tool below turns a quoted rate into a position-level cost, but the quote itself hides three details that decide what you actually pay.
First, the charge lands on notional, not on your margin. At high leverage the same rate takes a much bigger bite out of the capital you actually posted, which is why a "cheap" funding environment can still be the largest line item in a leveraged month. Second, you only pay at the settlement timestamp. Holding a position for seven hours across no settlement costs nothing in funding; holding it for one minute across the mark costs a full interval. Traders who close just before settlement and reopen just after are paying spread and fees to dodge funding, and that trade is usually worse than simply paying it.
Third, and most often missed: the rate is not a coupon, it is a live measure of how crowded one side is. A persistently high positive rate means longs are paying to stay long, which is a cost to you and a description of the market at the same time. When funding is expensive and open interest is climbing without spot volume behind it, the number in this calculator is telling you about the exit door as much as about your monthly bill.
Take the daily cost the calculator returns and divide it by your margin rather than your notional. Then ask how many days of that you would tolerate if price simply went sideways. For most leveraged positions the honest answer is a small number, and that number is your real holding period.
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fapi.binance.com /fapi/v1/premiumIndex · fetched live on page load and on every contract switch · nothing stored, nothing tracked · editing the rate by hand does not send a new request.
Two use cases.
Spot plus perp carry.
If you hold spot BTC and short an equal notional BTC perpetual, positive funding is the gross carry. The trade is not risk-free. Exchange risk, sudden negative funding, basis gaps, and forced deleveraging all matter.
Directional leverage.
If you hold a one-way long during a high positive funding period, the rate is a slow leak from margin. At 10x leverage, a +0.05% settlement rate can cost roughly 1.5% of margin per day before price even moves.
BTC traded into the $73,000 area while funding became expensive. A trader who entered late with leverage paid both price risk and funding drag. The calculator makes that hidden carry visible.
Local market note.
When The Block or CoinDesk writes that perp funding is elevated, run the actual rate through the calculator. A headline can tell you leverage is hot; your notional and leverage decide how much it costs you.