What You'll Learn in This Lesson
In this lesson you build the full chain from start to finish: how the Federal Reserve's interest rate moves the Dollar Index (DXY), how the Dollar Index moves the global gold ounce, and how that ounce, together with Tehran's free market dollar rate, sets the price of gold and coin in Iran's market. You'll also see which links in this chain are a calculable formula, and which is only a loose, background pressure, not a direct relationship.
Definitions
The Federal Funds Rate is the rate American banks follow when lending each other overnight reserves. The Federal Open Market Committee (FOMC), the policy making arm of the US central bank, sets this rate at eight regular meetings a year, and since 2008 has announced it as a range, or band, rather than a single fixed number. The committee's official mandate is twofold: price stability and maximum employment.
The Dollar Index (DXY), as you saw in Sahmino's previous lesson, measures the dollar's strength against a basket of six major currencies, dominated by the euro.
The global gold ounce is the pricing unit for gold in world markets; one troy ounce equals 31.1035 grams, and it is always priced in dollars.
Tehran's free market dollar rate is discovered in Iran's informal currency exchange market, based on the real supply and demand for cash and transfers; a rate separate from the official rate or the FX and gold exchange center's transfer rate.
The Chain, Link by Link
Link one: interest rate to Dollar Index. When the Fed keeps its rate high or raises it, holding dollars and dollar denominated bonds becomes more attractive to investors, because it offers a higher real return. Capital shifts from currencies like the euro and yen toward dollar assets, and that demand pushes the Dollar Index up, or at least keeps it from falling; the opposite happens when markets price in a rate cut.
As one example, at its July 2026 meeting the Federal Reserve held its rate steady in the 3.5 to 3.75 percent range for a fifth consecutive meeting, even though three committee members dissented, preferring a 0.25 point hike, a sign the door for a rate increase at the next meeting stayed open.
Link two: Dollar Index to the global gold ounce. Because gold is always priced in dollars, a stronger dollar means the same amount of gold costs more for non dollar buyers, and demand usually softens a little; that is why DXY and the global ounce tend to move in opposite directions across most periods (you saw this relationship in more detail in Sahmino's previous lesson).
Link three: the global ounce to Iran's gold and coin price. The price of a gram of gold in Iran comes from a multi step formula: the global ounce divided by 31.1035, multiplied by the free market dollar rate, multiplied by the purity factor (0.75 for 18 karat); a coin is priced on the same base, plus its own premium or discount (see the full formula in the "Pricing Gold in Iran" lesson).
A Worked Example
Suppose the Fed, contrary to market expectations, raises its rate by 0.25 points at its next meeting. If the market judges this "hotter than expected," the Dollar Index could climb close to 1.5 percent over a few days, for example from 100 to 101.5. If the usual inverse relationship with gold holds, the global ounce could fall by a similar share, near 1.5 percent, meaning roughly $4,350 down to about $4,285. If Tehran's free market dollar rate stays unchanged at 187,800 tomans over the same stretch, the price of a gram of 18 karat gold would also pull back by roughly the same share, from about 19,700,000 tomans to about 19,400,000 tomans; in other words, a Fed decision, without ever naming Iran, has reached a gold buyer's wallet in Tehran. This entire example is a labelled hypothetical; it only illustrates the calculation path, not a forecast.
Transmission to Iran's Market
This chain's first two links (rate to Dollar Index, and Dollar Index to the ounce) happen outside Iran and carry no ticker on any Tehran exchange board; their effect only reaches the domestic market through the global ounce figure inside the gold pricing formula. But the fourth link, Tehran's free market dollar rate itself, works differently: the Fed does not set that rate directly. It is built by Iran's own real currency supply and demand, liquidity, inflation expectations, and sanctions (you saw these four channels in full in the "What Moves the Dollar" lesson). US monetary policy creates, at most, a loose background pressure: when the dollar broadly strengthens against every world currency, competition among low reserve or sanctioned economies for that same scarcer hard currency tends to rise, but this is a tendency, not a formula with a fixed ratio.
A layer entirely independent of the Fed also sits on top of the coin: its premium or discount, meaning the gap between a coin's trading price and the intrinsic value of the gold inside it. As one example, per Sahmino's own tracked data, the Emami coin's premium, which had even turned negative days earlier, reached about 4,227,000 tomans by the evening of Tuesday, August 11, 2026 (20 Mordad 1405), a jump of nearly 52 percent overnight, with no connection to any Fed decision or the Dollar Index. That number is built by auction supply, domestic demand, and coin market psychology, not Washington.
Common Mistakes
Mistake one: assuming that when the Fed raises its rate, Tehran's free market dollar rate immediately follows suit. That rate is built by domestic supply and demand, not a decision in Washington.
Mistake two: treating the Dollar Index to gold relationship as a fixed law with a set ratio. In severe geopolitical shocks, both assets sometimes get bought together as safe havens, and the inverse relationship temporarily breaks down.
Mistake three: ignoring the coin premium or discount as an independent layer. As the example above showed, this figure can move tens of percent overnight with no Fed news at all.
Summary
A Fed decision is an American decision, but its footprint can be traced: from the interest rate to the Dollar Index, from the Dollar Index to the global gold ounce, and from that ounce, alongside Tehran's free market dollar rate, to the price of Iranian gold and coin. The two middle links in this chain follow a formula; the last link, Tehran's own dollar rate, is built by domestic factors. To see the previous link in this chain up close, visit Sahmino's lesson on the Dollar Index (DXY); for the full formula behind Iran's gold price, see Pricing Gold in Iran, and for what builds Tehran's dollar rate, see What Moves the Dollar? To browse every lesson in this series, visit the Sahmino Academy page.
