What happens if my partner and I can't agree on what the business is actually worth?

Start by checking your shareholders' agreement, since many include a mechanism for exactly this situation — a formula for calculating value, a process for appointing an independent valuator, sometimes with each side naming one and the two valuators agreeing on a third if needed, or a shotgun clause that sidesteps the valuation debate entirely by having one partner name a price and the other choose to buy or sell at it.

If your agreement is silent, or you don't have one, the practical path is usually to jointly retain, or each retain, an independent business valuator to produce a defensible number you can negotiate from, rather than continuing to argue over competing internal estimates. Persistent, serious disagreement over value combined with an inability to work together can sometimes escalate into broader disputes about the partnership itself, so it's worth trying to resolve the valuation question constructively and early, ideally with professional input, before positions harden further.