Monthly Tax Reserve Formula
Learn how to estimate a monthly tax reserve from business revenue, allowable expenses, estimated rates, and a buffer.
This calculation estimates the amount of monthly business profit to reserve for income tax and other profit-based contributions. It starts with profit after allowable expenses, applies the rates you enter, and then adds a buffer for uncertainty.
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Recommended Monthly Tax Reserve
Where:
Subtract allowable expenses from monthly revenue, apply the combined estimated tax and contribution rate to the remaining profit, then increase that amount by the selected buffer.
Variables Explained
| Variable | What It Means | Unit |
|---|---|---|
| monthlyRevenue - Monthly business revenue | Average monthly sales or professional income before business expenses. | currency |
| monthlyExpenses - Monthly allowable expenses | Estimated deductible business expenses for the month. | currency |
| incomeTaxRate - Estimated income tax rate | Estimated rate applied to taxable business profit. | percent |
| contributionRate - Other profit-based contribution rate | Estimated social insurance, self-employment, or similar contribution rate based on profit. | percent |
| reserveBufferRate - Extra reserve buffer | Additional percentage added to the estimated liability for planning uncertainty. | percent |
Step-by-Step Calculation
Estimate monthly taxable profit
Revenue less allowable expenses gives estimated profit. The maximum function prevents a negative taxable-profit result.
monthlyTaxableProfit = max(monthlyRevenue - monthlyExpenses, 0)
Combine the entered rates
The income tax rate and other contribution rate are added and converted from a percentage to a decimal.
combinedTaxRate = (incomeTaxRate + contributionRate) / 100
Calculate tax before the buffer
Apply the combined rate to estimated taxable profit.
monthlyTaxAndContributions = monthlyTaxableProfit * combinedTaxRate
Add the reserve buffer
The buffer increases the estimated liability by the selected percentage.
monthlyTaxReserve = monthlyTaxAndContributions * (1 + reserveBufferRate / 100)
Project an annual reserve
This annual figure assumes the same monthly profit, rates, and buffer for twelve months.
annualTaxReserve = monthlyTaxReserve * 12
Calculate profit after reserving
This is the estimated profit remaining after the recommended reserve is set aside.
monthlyProfitAfterReserve = monthlyTaxableProfit - monthlyTaxReserve
Example: freelancer monthly tax reserve
Monthly taxable profit
max(8,000 - 2,500, 0)
$5,500
Combined estimated rate
(25 + 10) / 100
0.35 or 35%
Tax and contributions before buffer
5,500 * 0.35
$1,925
Recommended monthly reserve
1,925 * (1 + 5 / 100)
$2,021.25
Estimated annual reserve
2,021.25 * 12
$24,255
Profit after reserve
5,500 - 2,021.25
$3,478.75
Final Result
Set aside approximately $2,021 per month, or $24,255 over a similar twelve-month period.
Assumptions
- ✓Monthly revenue and allowable expenses are reasonable estimates and are broadly consistent over the period considered.
- ✓The entered income tax and contribution rates apply to all estimated taxable profit.
- ✓The buffer is applied after the estimated tax and contribution amount is calculated.
- ✓The calculation is for planning and does not determine an actual tax liability.
Limitations
- !Actual tax calculations may use progressive rates, thresholds, credits, reliefs, losses, or adjustments that are not included here.
- !Tax rules, deductible expenses, rates, and payment timing vary by location and individual circumstances.
- !Revenue and expenses can fluctuate substantially, making a monthly annualized projection less reliable.
- !Sales taxes collected on behalf of tax authorities are not included in this profit-based reserve calculation.
Common Mistakes to Avoid
Calculating the reserve from total revenue instead of revenue less allowable business expenses.
Entering a percentage as a decimal, such as entering 0.25 instead of 25 for a 25% rate.
Including personal spending as an allowable business expense.
Forgetting to include a relevant profit-based contribution rate in the estimate.
Treating the annual projection as an actual tax bill when income changes during the year.
Related Formulas
Frequently Asked Questions
How is a monthly tax reserve calculated?
The calculator subtracts allowable expenses from revenue, applies the combined estimated tax and contribution rate, and adds the selected buffer.
Why does the formula use max with zero?
It ensures that expenses greater than revenue produce zero taxable profit for this estimate rather than a negative tax reserve.
Does the buffer increase the tax rate?
No. It increases the amount reserved after the estimated tax and contributions are calculated.
Can I use one combined rate instead of separate rates?
Yes. You can enter the full estimated combined percentage in one rate field and enter zero in the other, if that suits your planning method.
Does this formula include sales tax or VAT?
No. It is designed for income tax and other profit-based contributions. Amounts collected for sales taxes may need separate tracking.
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