A companion page on this site covers the negotiation of seller carry, why sellers do it and which clauses matter. This page covers the arithmetic, because once carry enters a deal, it stops being a term and becomes a layer of the capital stack, and the stack is where its real effects live.
The first effect is the one that motivates most carry conversations: the equity check shrinks. Whatever the seller carries is capital the buyer does not raise, and on deals where the coverage-constrained senior loan came in below hopes, carry is frequently the piece that closes the proceeds gap without a painful equity call. Less equity in the same deal mechanically concentrates the returns on the equity that remains, which is the levered-return story every carry pitch leads with, and it is true as far as it goes.
The second effect is the blended cost of capital, and it can cut either way. Carry priced below the senior rate, which motivated sellers sometimes accept because their alternative is a lower price, cheapens the whole debt stack. Carry priced above it buys proceeds at a premium, and whether that premium is worth paying depends on what the marginal dollar earns inside the deal. The comparison that matters is never carry rate against senior rate. It is carry rate against the return on the equity dollar it replaces, which is a number your model has and your instinct does not.
The third effect is the one the pitch omits: carry is leverage, and leverage is symmetric. A junior obligation with its own payment and its own maturity now sits in the deal's calendar, coverage must clear the combined debt service and not just the senior's, and the cushion between a good year and a covenant conversation got thinner in exchange for the smaller check. None of this argues against carry. It argues for modeling the stack as a stack, with each layer's cost, priority, and maturity doing its real work in the cash flows, rather than treating carry as free money that happens to charge interest.
The widget below runs the single-period sketch: price, senior terms, carry terms, and it returns the equity required with and without the carry, the blended cost of the debt, and the combined debt service. It will show you the shape of the trade in thirty seconds. What it cannot show is the trade over time, the year-three balloon landing mid-renovation, the coverage path as leases roll, the waterfall paying differently because the equity base changed, and that is the seam where PropCalc™ picks up, carrying the full multi-layer stack through every month of the hold. Structure is the cheapest source of returns in this business. It is also the cheapest source of surprises. The model is how you get the first without the second.