Excel Add-in Coming Soon

Calculate U.S. surplus lines taxes directly in Microsoft Excel with custom functions. Use formulas like =SLTAX.CALCULATE("Texas", 10000) just like native Excel functions!

🚀 Office 365 & Excel for Web

Works with Excel 2016+, Excel for Web, and Microsoft 365. Type formulas in any cell and get instant results—no VBA or macros required!

📥 Download Test Template 🔑 Get Your API Key

Pre-configured workbook with all functions + 100 free calculations included

Key Features

✨ Native Excel Experience

Autocomplete, formula bar, and works just like SUM or VLOOKUP

🌍 53 Jurisdictions

All 50 states + DC + Puerto Rico + Virgin Islands

📅 Historical Rates

Look up rates from any date for auditing

⚡ Real-time API

Always current rates, updated automatically

Requirements

Requirement Details
Excel Version Excel 2016+, Excel for Web, or Microsoft 365
Platform Windows, Mac, or Web browser
API Key Free account at app.surpluslinesapi.com
Internet Required for API calls

Installation

📋 Coming Soon to Office Store

The Excel Add-in is currently in development. Sign up for our newsletter to be notified when it's available!

Option 1: Office Store (Coming Soon)

  1. Open Excel
  2. Go to Insert → Add-ins → Get Add-ins
  3. Search for "Surplus Lines Tax"
  4. Click Add

Option 2: Sideload for Testing

  1. Download the manifest.xml file from our GitHub repository
  2. Open Excel
  3. Go to Insert → Add-ins → My Add-ins
  4. Click Upload My Add-in
  5. Select the manifest.xml file
  6. Click Upload

Configuration

Step 1: Get Your API Key

  1. Go to app.surpluslinesapi.com
  2. Sign in or create an account
  3. Copy your API key from the dashboard

Step 2: Configure the Add-in

  1. Click the Surplus Lines Tax button in the ribbon (Home tab)
  2. Paste your API key in the Settings panel
  3. Click Save API Key

Step 3: Start Using!

Type a formula in any cell:

=SLTAX.CALCULATE("Texas", 10000)

Result: 503

Function: SLTAX.CALCULATE

Calculate the total surplus lines tax for a given state and premium amount.

Syntax
=SLTAX.CALCULATE(state, premium)

Parameters

Parameter Type Required Description
state Text Yes State name or 2-letter code (e.g., "Texas" or "TX", "California" or "CA")
premium Number Yes Premium amount in USD

Returns

Total tax amount (number). The API response also includes state_code (2-letter abbreviation like "TX").

Example

=SLTAX.CALCULATE("Texas", 10000)
→ 503

=SLTAX.CALCULATE("TX", 10000)
→ 503 (state codes also work!)

=SLTAX.CALCULATE(A2, B2)
→ Calculates using values from cells A2 and B2

Function: SLTAX.CALCULATE_DETAILS

Get a detailed breakdown including state, premium, total tax, and total due. Returns 4 values that spill to adjacent cells.

Syntax
=SLTAX.CALCULATE_DETAILS(state, premium, [multiline])

Parameters

Parameter Type Required Description
state Text Yes State name or 2-letter code
premium Number Yes Premium amount in USD
multiline Boolean No If TRUE, returns data vertically (1 column). Default: FALSE (horizontal)

Returns

Array with: [state, premium, total_tax, total_due]

Example

=SLTAX.CALCULATE_DETAILS("California", 10000)
→ California | 10000 | 318 | 10318

=SLTAX.CALCULATE_DETAILS("California", 10000, TRUE)
→ Returns vertically (4 rows × 1 column)

Function: SLTAX.CALCULATE_WITHPREMIUM

Calculate tax and return premium, total tax, and total due. Returns 3 values.

Syntax
=SLTAX.CALCULATE_WITHPREMIUM(state, premium)

Parameters

Parameter Type Required Description
state Text Yes State name or 2-letter code
premium Number Yes Premium amount in USD

Returns

Array with: [premium, total_tax, total_due]

Example

=SLTAX.CALCULATE_WITHPREMIUM("Texas", 10000)
→ 10000 | 503 | 10503

Function: SLTAX.RATE

Get the current tax rate percentage for a specific state.

Syntax
=SLTAX.RATE(state)

Parameters

Parameter Type Required Description
state Text Yes State name or 2-letter code (e.g., "California" or "CA")

Returns

Tax rate as a percentage (e.g., 3 for 3%). Response includes state_code.

Example

=SLTAX.RATE("California")
→ 3

=SLTAX.RATE("TX")
→ 4.85 (state codes work!)

Function: SLTAX.RATES

Get tax rates for all 53 states. Returns a 2-column array with state names and rates.

Syntax
=SLTAX.RATES()

Returns

2-column array: [state, rate] for each jurisdiction (53 rows × 2 columns)

Example Output

=SLTAX.RATES()

Returns (fills 53 rows × 2 columns):
| State         | Rate  |
|---------------|-------|
| Alabama       | 6     |
| Alaska        | 2.7   |
| Arizona       | 3     |
| ...           | ...   |
| Texas         | 4.85  |
| ...           | ...   |
| Wyoming       | 3     |

Function: SLTAX.RATES_DETAILS

Get detailed tax rate information for all states including all fee components. Returns an 11-column array.

Syntax
=SLTAX.RATES_DETAILS()

Returns

11-column array with complete fee breakdown for each state (53 rows × 11 columns):

  • State, Tax Rate, Stamping Fee, Filing Fee, Service Fee
  • Surcharge, Regulatory Fee, Fire Marshal Tax, SLAS Fee
  • Flat Fee, Legislative Source

Example

=SLTAX.RATES_DETAILS()

Returns (fills 53 rows × 11 columns):
| State  | Tax Rate | Stamping | Filing | Service | ... |
|--------|----------|----------|--------|---------|-----|
| Alabama| 6%       | 0.1%     | $10    | null    | ... |
| ...    | ...      | ...      | ...    | ...     | ... |

Function: SLTAX.STATES

Get a list of all 53 supported jurisdictions. Returns a vertical array.

Syntax
=SLTAX.STATES()

Returns

Vertical array of 53 state names (one per cell)

Example Output

=SLTAX.STATES()

Returns (fills 53 rows × 1 column):
| State         |
|---------------|
| Alabama       |
| Alaska        |
| Arizona       |
| ...           |
| Texas         |
| ...           |
| Wyoming       |

Function: SLTAX.HISTORICALRATE

Get the tax rate that was in effect for a specific state on a given date. Useful for auditing past policies.

Syntax
=SLTAX.HISTORICALRATE(state, date)

Parameters

Parameter Type Required Description
state Text Yes State name or 2-letter code (e.g., "Iowa" or "IA")
date Text/Date Yes Date in YYYY-MM-DD format or Excel date

Example

=SLTAX.HISTORICALRATE("Iowa", "2025-06-15")
→ 0.95

=SLTAX.HISTORICALRATE("IA", "2025-06-15")
→ 0.95 (state codes work!)

Function: SLTAX.HISTORICALRATE_DETAILS

Get detailed historical tax rate information for a specific state and date, including all fee components and effective dates.

Syntax
=SLTAX.HISTORICALRATE_DETAILS(state, date, [multiline])

Parameters

Parameter Type Required Description
state Text Yes State name or 2-letter code
date Text/Date Yes Date in YYYY-MM-DD format or Excel date
multiline Boolean No If TRUE, returns data vertically (15 rows). Default: FALSE (horizontal)

Returns

15-column array with: state, date, tax_rate, stamping_fee, filing_fee, service_fee, surcharge, regulatory_fee, fire_marshal_tax, slas_clearinghouse_fee, flat_fee, effective_from, effective_to, legislative_source, confidence

Example

=SLTAX.HISTORICALRATE_DETAILS("Texas", "2024-01-01")
→ Texas | 2024-01-01 | 4.85% | 0.18% | ... (15 columns)

=SLTAX.HISTORICALRATE_DETAILS("Texas", "2024-01-01", TRUE)
→ Returns vertically with labels (15 rows × 1 column):
   State: Texas
   Date: 2024-01-01
   Tax Rate: 4.85%
   ...

Test Template

Download our pre-configured Excel workbook to quickly test all functions. The template includes 5 worksheets with example formulas.

📥 Download Test Template

What's Included

  • Calculator Sheet — Tax calculations with SLTAX.CALCULATE, CALCULATE_DETAILS, and CALCULATE_WITHPREMIUM
  • Rates Sheet — Single state rate lookups and complete rates table
  • All States Sheet — Complete list of 53 jurisdictions
  • Detailed Rates Sheet — Full fee breakdown with SLTAX.RATES_DETAILS
  • Historical Sheet — Historical rate lookups with SLTAX.HISTORICALRATE and HISTORICALRATE_DETAILS

Quick Start

  1. Download the template above
  2. Install the Surplus Lines Tax Add-in (see Installation)
  3. Configure your API key
  4. Open the template—formulas will calculate automatically!

Usage Examples

Simple Tax Calculation

A B C
State Premium Tax
Texas 10000 =SLTAX.CALCULATE(A2, B2)
California 25000 =SLTAX.CALCULATE(A3, B3)

Detailed Breakdown

=SLTAX.CALCULATE_DETAILS("California", 10000)

Results in 4 cells:
| California | 10000 | 318 | 10318 |

Create a Rate Reference Table

=SLTAX.RATES()

Automatically fills a 53-row, 2-column table with all states and their rates.

Troubleshooting

"API key not configured"

Open the Settings panel (click the Surplus Lines Tax button in the ribbon) and enter your API key.

Functions not appearing

  1. Make sure the add-in is loaded (check Insert → Add-ins)
  2. Try restarting Excel
  3. Type =SLTAX. and check if autocomplete appears

"#VALUE!" error

Check that:

  • State name is valid (use full names like "Texas" or 2-letter codes like "TX")
  • Premium is a positive number
  • You have API credits remaining

FAQ

Does it work on Mac?

Yes! The add-in works on Excel for Mac, Windows, and Web.

Do I need a Microsoft 365 subscription?

The add-in works with Excel 2016 or later, including standalone versions. Microsoft 365 is not required but recommended for the best experience.

How is this different from Google Sheets?

This is a native Excel add-in with proper custom functions (like built-in Excel functions). Google Sheets uses Apps Script. Both provide the same calculation functionality.

Can I use state abbreviations?

Yes! You can use either full state names (e.g., "Texas") or 2-letter state codes (e.g., "TX"). Both formats work in all functions.

Pricing

  • 100 free calculations included when you sign up
  • $0.38 per calculation after free tier
  • $18/month minimum for active accounts
  • $50 initial deposit (credited to your balance)
  • Add credits anytime at app.surpluslinesapi.com

Need help? Contact us at support@undtec.com

© Underwriters Technologies 2025