First you need to know your cost basis, both now and when you sell. Your cost basis is what you paid for the home plus what you paid for permanent improvements. (You can't include the value of work you did, only money you paid for supplies or other people's labor.)
Then, the basis for depreciation is either the cost basis or the fair market value, whichever is lower, as of the date the property is placed in service, minus the value of the land.
If you think the land valuation is incorrect, you can get an appraisal from a local real estate professional.
The issue with depreciation and recapture is really complicated and there is no simple answer. You have to think about things like the concept of the present value of money. Suppose you use a high land valuation, 40%, and you own the property for 20 years. You will have deducted maybe $113,000 as depreciation. Or suppose you use a low land valuation of 20%, you will have deducted $151,000. Paying tax on $113K in the year you sell is easier on the wallet than paying recapture tax on $151K, but it's not that simple.
Recapture is taxed at regular income tax rate but is capped at 25%. Suppose you are in the 32% tax bracket now; the deduction saves you 32% now but will be repaid at 25% later. Or suppose you are in the 22% bracket both now and when you sell, and you save 22% now and repay 22% later. That sounds like a wash but its not, because for those 20 years, you will be able to use that money (about $1600 per year) for other useful things, like investing or buying more property. Thanks to inflation, money you repay later is worth less than it is today even if the dollar amount is nominally the same. (If you claimed $151,000 in depreciation over 20 years, you would save $1600 per year on your taxes, and owe $33,000 in recapture tax when you sell, at the 22% rate. If you invested that $1600 per year in tax-free muni bonds at 3%, you would have a total of $45,000 from which to repay the $33,000.)
And if you were to die and leave the property to your children, they would receive a stepped up basis and not have to pay any recapture tax.
So there is an argument for taking as much depreciation as you can while you can. I can't tell you which is better in your specific situation.
