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Corporate Finance

How much should a firm borrow?

Follow tax savings, buybacks and the costs of financial distress to see what shapes a borrowing decision. Solve has 10 questions on tax shields, firm value and lender–shareholder incentives.

Tax savings · Step 1 of 12

Interest changes the split of operating income

Operating income split between lenders, shareholders and government
No debt: total $300kWith debt: total $300k
SharesTaxNo debtLendersSharesTaxWith debt
No debt · Lenders: $0No debt · Shares: $225kNo debt · Tax: $75kWith debt · Lenders: $108kWith debt · Shares: $144kWith debt · Tax: $48k
No debt, total $300k; Lenders $0, Shares $225k, Tax $75k. With debt, total $300k; Lenders $108k, Shares $144k, Tax $48k
Mothglass Machines is a made-up firm with operating income (EBIT) of $300,000 each year. In this example, interest is deducted before corporate tax, and all remaining profit goes to shareholders. Ignore personal taxes and distress costs for now.
Try it: Move the debt amount, then compare the tax slices.
Debt at the given annual rate of 6%$1.8M
Interest
$108k
Tax saved
$27k
Investor cash
$252k
Interest = rD × D = (6% × $1,800,000) = $108,000.
No debt: tax = (25% × $300,000) = $75,000; shares receive $225,000.
With debt: tax = (25% × (300,000 − 108,000)) = $48,000.
Shares = ((300,000 − 108,000) × (1 − 25%)) = $144,000.
Total investor income = (108,000 + 144,000) = $252,000.
With debt minus without debt = (252,000 − 225,000) = $27,000. Investor income rises.
Check yourself
With full use of the interest deduction, which formula always gives the increase in total lender plus shareholder income?

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