Excel-like software for performing calculations on a website

I have a pretty extensive Excel spreadsheet with many formulas used to calculate 10 and 15-year financial projections on real estate acquisitions. I'm looking for a web-based software solution that could replicate the types of financial calculations that Excel can perform but can do it for a large number of customers.

I'm not looking to publish my spreadsheet to Excel Online or distribute the spreadsheet, I'm looking for a commercial product that can perform the same/similar financial calculations for a large set of customers. Many of the products I've looked into are better at analyzing data but I've not been able to find one that definitively says that it supports much of the Excel calculation and functional capabilities.

I'm also not looking to use one of the commercial products that have already hard-coded their financial projections into a product offering. I'm developing a solution where this feature is only a part of a larger software service.

Has anyone come across something that is fully customizable and is offered as a back-end server/solution that can perform Excel-like calculations?

Tableau would be where I would start looking first.

Thanks, I should have mentioned them specifically because I've looked into them and they were one of those that I was referring to regarding their proficiency at presenting and analyzing data, but I have not been able to get them to tell me how they compare to Excel in performing calculations across many different and simultaneous multi-row/column calculations. I have requested their free demo but from what I've been able to determine, they aren't up-front about their financial calculation ability.

Great charts and dashboards though.