Strip away every indicator and forex has one underlying engine: capital flows toward yield. If holding dollars pays 5% while holding yen pays 0.5%, there is a standing 4.5% incentive to sell yen and hold dollars, every single day, before price even moves. That incentive is the interest rate differential, and it is the closest thing currency markets have to gravity.
It works on two timescales. Day to day, the differential is the carry: long the higher-yielding currency of a pair, you are paid to wait; short it, you pay to wait. Over months, DIFFERENCES in central bank paths move the differential itself, and pairs re-price to follow. The largest trends in modern FX, like USD/JPY's climb while the Fed hiked and the Bank of Japan held near zero, are rate-differential stories at their core.
What matters more: the level or the change
The level of the differential sets the standing pressure and the cost of fighting it. The CHANGE in expectations is what produces the sharp moves: a central bank turning hawkish while its counterpart stays put widens the expected differential, and the pair usually starts moving well before the actual rate decision lands.
This is why rate differentials belong in a macro score but should not BE the score. They are slow, they are occasionally overridden for months by risk sentiment (funding currencies like the yen strengthen violently in risk-off even against wider differentials), and around policy turning points the published rate lags the market's expectation.
How KairosBias uses them
Each of the 8 majors carries a rates sub-score built from its central bank policy rate relative to the rest of the majors, refreshed from primary sources. It contributes 15% of the composite score, deliberately the smallest of the four layers: enough that a wide, persistent differential keeps leaning on the score, small enough that a fast trend or positioning shift is not drowned out by a slow-moving rate. The full weighting is on the methodology page, and the per-currency sub-scores are visible on the meter.
Common questions
The gap between the interest rates of the two currencies in a pair. It determines the carry (what you are paid or pay daily to hold the position) and, when expectations about it shift, it drives multi-month trends as capital moves toward the higher-paying currency.
Higher rates increase the return on deposits and bonds denominated in that currency, attracting capital inflows. The effect is strongest when the hike widens the gap versus other major central banks, and markets usually price the move in as soon as expectations shift, before the decision itself.
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Four of the 8 major currencies scored from EMA structure, COT positioning, momentum and rate differentials, refreshed every 4 hours. No card, no expiry.
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