Can expense be written off before business starts?

Yes, but only partially. Depending on the type of equipment it is, you'll have to depreciate it over a certain period of time. How quickly you can depreciate it for tax purposes may vary.

You probably won't be able to benefit from the tax reduction due to depreciation expense unless you have "passive income" from another source. It may depend on the legal structure of your business. If it's a sole proprietorship, I'm pretty sure that's the case.

These types of expenses will offset passive income and reduce your tax liability for this income alone. You'll have to wait until you have passive income in order to benefit from the tax write down. You can, however, build up a reserve passive losses to offset future passive income.

In any case, you'll want to consult a good tax accountant if you're counting on the tax write off.

This is why people use accountants. You think EQUIPMENT is an expense? The government may disagree, and consider it an asset. You can choose to claim the depreciation each year as a tax deduction, or you may be able to claim it all. See, complicated.

If you want to risk a tax audit, sure, buy the stuff and claim it all as a business expense, without generating any business revenue, and see how fast the IRS comes down on you.

Equipment is an Asset

Paying the Office Lease or employee salaries are an Expense

You can begin to depreciate your equipment the day you buy it just as you could deduct rent you paid for your facility even if you didn't yet open the door.