Introduction
Microsoft's effective tax rate for the year to June 2025 was 17.6%, well below the 21% federal statutory rate. In the same year it paid $28.7 billion of income taxes, about $6.9 billion more than the $21.8 billion provision in its income statement. Two different gaps, with two different causes. The first comes from items that are taxed differently from how they are booked and never come back into line, such as profits taxed at Ireland's lower rate and the federal research credit. The second comes from items that are booked and taxed in different years, chiefly research costs that the tax law required Microsoft to capitalize and deduct over five years (15 for research done abroad) while its books expensed them at once.
Accountants call the first kind permanent differences and the second temporary differences. The distinction decides how each difference is recorded and where it shows up, and it is the key to reading any company's tax note. The broader reasons that book and taxable income diverge are covered in book vs tax accounting.
Two Kinds of Difference
Accounting Standards Codification (ASC) 740, the US standard on income taxes, approaches the question from the balance sheet. Every asset and liability has a carrying amount in the books and a tax basis, the amount at which the tax authorities recognize it. Where the two differ, recovering the asset or settling the liability will produce taxable or deductible amounts in the future.
- Temporary difference
A difference between the carrying amount of an asset or liability in the financial statements and its tax basis that will result in taxable or deductible amounts in future years, when the asset is recovered or the liability settled. Temporary differences give rise to deferred tax assets and liabilities.
Temporary differences come in two directions. A taxable temporary difference, such as an asset with a carrying amount above its tax basis after accelerated tax depreciation, will increase future taxable income and creates a deferred tax liability. A deductible temporary difference, such as a warranty reserve that is expensed in the books but deductible only when paid, will reduce future taxable income and creates a deferred tax asset. Both are measured at the enacted tax rate expected to apply when they reverse, as explained in deferred tax liabilities.
Permanent differences have no balance sheet counterpart. A fine paid to a regulator is an expense in the books but will never be deductible; interest on a municipal bond is income in the books but will never be taxed. Because nothing reverses, there is no future tax effect to record. The difference simply changes this year's tax relative to book income, and so changes the effective tax rate.
Common Examples
The type of any item follows from one question: will it ever be both booked and taxed? Depreciation, reserves, capitalized research and leases are all recognized on both sides in the end, so they are temporary. Fines, excess executive pay and municipal interest are recognized on only one side, so they are permanent.
| Item | Type | Effect |
|---|---|---|
| Accelerated tax depreciation | Temporary, taxable | Deferred tax liability |
| Warranty, bad debt and other reserves | Temporary, deductible | Deferred tax asset |
| Research costs capitalized for tax | Temporary, deductible | Deferred tax asset |
| Lease liabilities and right-of-use assets | Temporary, both directions | Deferred tax asset and liability |
| Unrealized gains on investments | Temporary, taxable | Deferred tax liability |
| Fines and penalties | Permanent | Raises the effective rate |
| Executive pay above the Section 162(m) limit | Permanent | Raises the effective rate |
| Tax-exempt municipal bond interest | Permanent | Lowers the effective rate |
| Research and other tax credits | Rate item, like a permanent difference | Lowers the effective rate |
| Foreign income taxed at lower rates | Rate item | Lowers the effective rate |
Strictly, tax credits and foreign rate differences are not differences in income at all: they change the tax on the same income. They behave like permanent differences, though, appearing in the rate reconciliation rather than in deferred taxes, and bankers usually group them together as the items that explain the effective rate.
The Two Effects in Numbers
Take a company with $1,000 of pre-tax book income and a 25% tax rate, and add one difference at a time:
| Scenario | Taxable income | Current tax | Deferred tax | Total tax expense | Effective rate |
|---|---|---|---|---|---|
| No differences | 1,000 | 250 | 0 | 250 | 25.0% |
| 40 of non-deductible fines | 1,040 | 260 | 0 | 260 | 26.0% |
| 60 of tax-exempt interest in book income | 940 | 235 | 0 | 235 | 23.5% |
| 100 of extra tax depreciation | 900 | 225 | 25 | 250 | 25.0% |
The permanent differences change total tax expense and the effective rate, with no deferred tax. The temporary difference leaves total tax expense and the effective rate untouched: it lowers current tax by $25 and adds $25 of deferred tax expense, recording a deferred tax liability that will reverse when the depreciation catches up. Temporary differences change the timing of cash taxes; permanent differences change the amount, and with it the effective rate, the measure explained in effective, statutory and cash tax rates.
Microsoft's Two Gaps
Microsoft's 2025 annual report shows both kinds of difference at work. Its rate reconciliation, which captures the permanent and rate items, moves from 21.0% to 17.6%:
- Foreign earnings taxed at lower rates: minus 1.5 points, mostly from its regional operations center in Ireland, which generated 81% of its foreign pre-tax income.
- Foreign-derived intangible income deduction: minus 1.0 point.
- Research and development credit: minus 1.1 points.
- Excess tax benefits from stock-based compensation: minus 0.9 points.
- State income taxes, net of federal benefit: plus 1.5 points.
- Interest, net: plus 1.0 point; other items net to minus 1.4 points.
Its deferred tax balances capture the temporary differences. The largest deferred tax asset, for capitalized research and development, rose from $11.4 billion to $16.9 billion during the year: each year of capitalization added more future deductions than amortization used up. That build-up is the main reason cash taxes of $28.7 billion, 23.2% of pre-tax income of $123.6 billion, ran above the book provision. When the deductions are taken, the asset reverses and cash taxes fall below the provision, the pattern the 2025 change in US law has accelerated by allowing domestic research costs to be deducted immediately again.
Exceptions and Gray Areas
A few differences that look temporary are deliberately not recorded as deferred taxes:
- Non-deductible goodwill: goodwill from a stock acquisition has no tax basis, but ASC 740 prohibits recording a deferred tax liability on it, which would only increase goodwill in a circular way. The difference behaves like a permanent one, and a later goodwill impairment carries no tax benefit.
- Investments in foreign subsidiaries: a parent's book investment in a foreign subsidiary can exceed its tax basis, an outside basis difference. No deferred tax liability is recorded if the parent intends and is able to reinvest the earnings indefinitely.
Deloitte's discussion of outside basis differences explains how the 2017 tax act shrank these differences for US companies: it taxed most accumulated foreign earnings and largely exempted future dividends, though withholding taxes and currency effects can still create a liability. Microsoft's balance sheet carries a $1.1 billion deferred tax liability for foreign earnings. The goodwill exception is covered from the deal side in asset write-ups and deferred taxes in M&A.
Stock-based compensation is the hybrid. The book expense creates a deductible temporary difference and a deferred tax asset, but the eventual deduction depends on the share price when the award vests or is exercised. Any excess or shortfall relative to the deferred tax asset goes straight to the income statement, behaving like a permanent item, which is why it appears in Microsoft's rate reconciliation.
Why the Distinction Matters
For forecasting, the two kinds of difference feed different lines. Permanent and rate items set the effective tax rate, and therefore net income and earnings per share (EPS): a company whose low rate rests on foreign profits or credits will keep it only as long as those conditions last. Temporary differences set the gap between book tax and cash tax: their direction and reversal decide whether the cash a company pays in tax will run above or below the expense it reports.
Deferred tax assets also need a test that permanent differences do not: they are worth something only if the company will have enough future taxable income to use them. Where that is in doubt, a valuation allowance reduces them, covered in deferred tax assets and valuation allowances.
